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THE 



ASTROIOii^ 



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THE FACTS DEVELOPED 



ODEJRN ASTRONOMY, 



COLLKCTLD FOR 



THE tJSE 01 SCHOOLS 



E GENERAL READER. 



BY JOHN S. C. ABBOTT, 



1 


AUTHOF 

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. OF " MOTHER AT HOME," AND 


1 CRILD 


AT HOME." 


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LADELPIIIA.- 

BOSTON. 


W Y R i : 
AND I 

B r o a d w • y . 
-JAMES M. 
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KELT. 


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PBELL. 


1846. 





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# LIBRARY OF CONGRESS.} 

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i UNITED STATES OP AMERICA. i 




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THE 



YOUNG ASTRONOMER; 



THE FACTS DEVELOPED 



MODERN ASTRONOMY, 



COLLECTED FOR 



THE USE OF SCHOOLS 



THE GENERAL READER. 






BY JOHN S. C. ABBOTT, 

AUTHOR OF "MOTHER AT HOME," AND "CHILD AT HOME." 



NEWYORK: 
SAXTON AND MILES, 

205 Broadway. 

PHILADELPHIA.— JAMES M. CAMPBELL. 

BOSTON. SAXTON AND KELT, 







:^\ 



V I Y*\ a 

, A' 13 

\ 24s 



Entered according to the Act of Congress, in the year 1846, by 

JOHN S. C. ABBOTT, 

In the Clerk's Office of the District Court for the Southern District 
of New York. 



JENKINS, STEREOTYPES, AND PRINTER, 

114 Nassau street. 



A> > 



V 






PREFACE. 



Most treatises upon Astronomy contain much which is 
quite unintelligible to those who have not passed through a 
regular course of mathematical studies. It is, however, 
very desirable that all the youth in our schools should be 
familiar w r ith those simple yet sublime facts, which have 
been developed by this science. To present these facts in 
language which can be comprehended by every good under- 
standing in our common schools and academies, is the object 
of this work. It is hoped that these pages may incite a 
deeper interest in the study of this most noble of all the sci- 
ences ; that it may disseminate widely, in the popular mind, 
an acquaintance with those truths which are so eminently 
calculated to elevate the understanding, and to ennoble the 
heart ; and that many may be induced to prosecute the study 
into those higher regions of mathematical inquiries, which 
can call into requisition all the energies of a Newton and a 
Herschel. 



CONTENTS, 



CHAPTER I. 

GENERAL VIEW OF THE SOLAR SYSTEM. — THE SUN. 

General view of the Solar System — The Ptolemaic theory — The 
Copernican theory — The Planets, how distinguished — Comets 
— Proportionate magnitudes of the Planets — The Sun, its con- 
stitution ; probably inhabited — Rotation of the Sun ; revolution 
in its orbit — Spots on the surface of the Sun — Face of the Sun — 
Eclipse of the Sun — Distance from the Earth — Mode of ascer- 
taining its distance — Influence of the Sun's rays — Arguments 
in favor of the Sun being inhabited, ..... 



CHAPTER II. 

THE PLANETS MERCURY VENUS — THE EARTH. 

Primary Planets — Secondary Planets — Mercury, its distance from 
the Sun ; its size — The population Mercury could sustain — 
Length of a year upon Mercury — Length of a day — Atmosphere 
of Mercury— Venus, its distance from the Sun — Size of Venus — 
The diurnal and annual revolution of Venus — The mountains 
and atmosphere of this planet — Satellites — The population Ve- 
nus could sustain — The Earth ; its size ; its revolutions ; its 
form ; its orbit — The Equinoxes — Population of the Earth — 
Latitude — Longitude — Mode of ascertaining latitude and longi- 
tude, 24 



VI CONTENTS. 

CHAPTER III. 

THE MOON — MARS. 

Distance of the Moon from the Earth ; its size ; its revolutions ; 
its surface — Volcanoes in the Moon — The Moon's atmosphere 
— Eclipses of the Moon — Supposed influence of the Moon upon 
the weather, diseases, &c. — Is the Moon inhabited ? — The tides 
—Mars, its distance ,* rapidity of its motion — The diurnal and 
annual revolution of Mars, 40 

CHAPTER IV. 

VESTA — ASTREA — JUNO CERES — PALLAS JUPITER. 

The Asteroids ; how discovered ; place of their orbits ; theory 
respecting them — Vesta ; its size ; period of its revolution ; 
when discovered — Astrea ; when discovered ; its distance from 
the Sun — Juno; its size ; the population it could sustain ; pe- 
riod of its revolution ; its atmosphere — Ceres ; its size ; extent 
of surface ; population it could sustain ; its atmosphere ; its 
revolutions — Pallas ; its supposed size — Meteoric stones, how 
accounted for — The atmospheric hypothesis — The volcanic hy- 
pothesis— The lunar hypothesis — The nebular hypothesis — The 
planetary hypothesis — Jupiter ; its year ; its day ; its distance 
from the Sun ; its magnitude ; its equable temperature ; its 
atmosphere — The belts of Jupiter — The moons of Jupiter — 
Eclipses of Jupiter's satellites ; scenery, . ' . . .52 



CHAPTER V. 

SATURN — HERSCHEL, OR URANUS. 

Saturn ; its distance from the Sun ; its magnitude ; its diurnal 
annual revolution — Satellites of Saturn — Rings of Saturn — 
Magnitude of Saturn's rings — Character of the rings — Probably 
inhabited — Herschel ; by whom discovered ; its distance from 
the Sun ; its magnitude ; its probable temperature — Satellites 
of Herschel — Possible population of all the planets — Magni- 
tude of the Sun, 65 



CONTENTS. Vll 

CHAPTER VI. 



Comets ; their physical constitution — Newton's opinion — Size of 
Comets ; their number ; their periodic revolutions ; the pur- 
poses they are intended to subserve — Newton's opinion — Na- 
ture of their light, . . 75 

CHAPTER VII. 

THE FIXED STARS. 

Fixed Stars; their number — Constellations — Magnitude of the 
Stars — Sirius — Vega — Classification of Stars — Variety in the 
structure of the Stars — Color of the Stars — Distance of the 
Stars — New Stars and lost Stars — Opinions of Mrs. Sommer- 
ville, La Place and Dr. Good — Variable Stars — Theories to ac- 
count for Variable Stars — Double Stars — Colored Suns — Triple 
and multiple Stars — Our Firmament, * 82 

CHAPTER VIII. 

OBSERVATION. 

Difficulties under which Astronomical discoveries and investiga- 
tions are made — Appearance of the heavens to an observer on 
the Earth — Apparent motions of the Stars — The meridian — 
Importance of this line — Effect of the position of the observer 
on the apparent motions of the heavenly bodies — Apparent 
motions of the Sun and Stars at the equator ; at the poles ; at in- 
termediate positions — Altitude — Latitude — Ferguson's instru- 
ment — Simple observations which may be made by the pupil, 105 

CHAPTER IX. 

INSTRUMENTS AND OBSERVATORIES. 

Exactness necessary in Astronomical observations — Royal Obser- 
vatory at Greenwich — The telescope— Principle of its con- 
struction — Reflecting telescopes — Herschel's great telescope — 
The Rosse telescope — Difficulties in manufacturing large spe- 
cula — Annealing — Loss of Light — Lenses — Experiment to il- 
lustrate their refracting powers — Achromatic lenses — Diffi- 
culties in using a telescope — Tremors — Adjustments — State of 
the atmosphere — The finder — Interesting objects to be viewed 
—Transit instruments — Clock — Equatorial instruments, .117 



Viii CONTENTS. 



CHAPTER X. 



PRACTICAL RESULTS. 

Uses of Astronomy in Navigation — Instruments used by Naviga- 
tors — The quadrant — The sextant — Observations made on board 
ship at noon — Mode of obtaining the Latitude — Longitude — Re- 
lation of longitude to time — Illustrations of this — Signal made 
at Greenwich to give the ships in the port of London their 
time — Lunar observations, and design of them — Singular phe- 
nomenon in respect to the length of the day at sea — Advantages 
which have resulted to mankind from the science of Astron- 
omy, 132 



THE 



YOUNG ASTRONOMER, 



CHAPTER I. 

GENERAL VIEW OF THE SOLAR SYSTEM. 

THE SUN. 

The science of Astronomy treats of the motions, 
magnitudes and distances of the heavenly bodies. 
From the earliest ages of the world the stars have at- 
tracted attention ; and shepherds on the hillside, as 
they watched their flocks by night, and philosophers, 
on their housetops, have observed their apparent mo- 
tions, counted their numbers, and endeavored to ar- 
range them into classes or fanciful groups, which they 
called Constellations. 

The theory of Astronomy which has almost univer- 
sally prevailed until within the last four hundred 
years, is called the Ptolemaic theory. It receives this 
name from Ptolemy, its most distinguished advocate. 
Ptolemy lived about two hundred years after the birth 



Of what does Astronomy treat ? How long has Astronomy engaged 
attention ? Who have particularly watched the stars ? What are groups 
of stars called ? What theory of Astronomy has formerly prevailed ? 
Why is the Ptolemaic theory so called ? When did Ptolemy live ? 
1* 



10 THE YOUNG ASTRONOMER. 

of Christ. The Ptolemaic theory of Astronomy places 
the Earth in the centre of the universe, and supposes 
the Sun and the stars to revolve around it. 

The theory now universally received, is called the 
Copernican theory. Copernicus, who established this 
theory, lived about four hundred years ago. The 
Copernican theory is, that the Sun is the centre, around 
which the Earth, and all the planets of the Solar sys- 
tem revolve. It also supposes that the fixed stars are 
suns and centres, around which other systems revolve. 

The Solar system includes the Sun, and all the heav- 
enly bodies which revolve around it. Those bodies 
which, revolving around the Sun, shine, not by their 
own, but by reflected light, are called planets. The 
innumerable other glittering bodies which twinkle in 
the firmament, and which are immovable in their rela- 
tive position, and which shine not by reflected, but by 
their own light, are called fixed stars. The planets 
can be usually distinguished from the fixed stars by their 
mild, moon-like light, while the stars shine with a 
more intense and twinkling lustre. The planets are 
supposed to be worlds, somewhat resembling our own. 
The fixed stars are considered as suns. They are at 
such an immense distance, that even the telescope 
does not reveal to our view the revolving worlds to 
which they dispense light and heat. 

What is the Ptolemaic theory ? What is the present theory of As- 
tronomy called ? Who established this theory ? When did he live ? 
What is the Copernican theory ? What does the Solar system include ? 
What are planets ? What are fixed stars ? How can the planets be dis- 
tinguished ? How can the stars be distinguished ? What are the planets 
supposed to be ? What are the stars supposed to be ? Why do we not 
see the planets which are supposed to revolve around the stars ? 



GENERAL VIEW OF THE SOLAR SYSTEM. 11 

There are connected with the Solar system, besides 
the planets, vast bodies, called comets, of whose physi- 
cal structure and constitution, comparatively little is 
known. They pass around the Sun, and then disappear 
in the depths of space, and after the lapse, perhaps, of 
many centuries, reappear, alarming the ignorant by 
their portentous aspect in the sky. It has been sup- 
posed that the comets may connect tw T o or more systems 
together, by revolving around the suns which are the 
centres of those systems. 

It is difficult from diagrams to attain any very cor- 
rect conception of the Solar system. The following 
striking illustration, of the proportionate magnitudes 
and distances of the bodies composing the Solar sys- 
tem, has been given by Herschel. Let the Sun be re- 
presented by a globe two feet in diameter. At eighty- 
two feet distant put down a grain of mustard seed, and 
you have the size and place of the planet Mercury. 
At the distance of one hundred and forty-two feet lay 
down a pea, and it will represent Venus. Two hun- 
dred and fifteen feet from the central globe place an- 
other pea of about the same size, and it will represent 
the Earth. At the distance of three hundred and 

What bodies besides planets are connected with the Solar system ? 
What is said of their physical structure and constitution ? After pass- 
ing around the Sun where do they go ? What has it been supposed that 
comets connect ? Do diagrams give a correct idea of the Solar system ? 
Who has given a striking illustration of the bodies composing this sys- 
tem? By what would Herschel represent the Sun ? At what distance 
would he place Mercury ? What would represent its proportionate 
magnitude ? At what distance would he place Venus ? What would 
represent the proportionate magnitude of Venus ? At what distance 
would he place the Earth ? What would represent the proportionate 
magnitude of the Earth ? 



12 



THE YOUNG ASTRONOMER. 



twenty-seven feet place a pin's head, and it will repre- 
sent the planet Mars. About five hundred feet from 
the Sun, place five of the smallest grains of sand, to 
represent Vesta, Astrea, Juno, Ceres and Pallas, 
which are called the Asteroids. At a quarter of a 
mile from the globe which represents the Sun, place 
an orange of a middle size, and it will represent 
Jupiter. An orange a little smaller, two-fifths of a 
mile distant, will represent Saturn. And Herschel 
would be represented by a cherry, three quarters of a 
mile distant. It will at once be perceived that by or- 

COMPARATIVE MAGNITUDES OF THE PLANETS. 




By what would Mars be represented ! At what distance ? Where 
would the Asteroids be placed ? By what would they be represented ? 
At what distance should Jupiter be placed ? By what should it be re- 
presented ? Where should Saturn be placed ? What would represent 
its size ? What would represent the size of Herschel ? At what dis- 
tance should it be placed ? 



GENERAL VIEW OF THE SOLAR SYSTEM. 



13 



dinary orreries and diagrams, but a feeble idea can be 
communicated of the comparative magnitude and dis- 
tances of the worlds which compose the Solar system. 
The accompanying diagram may, however, give the 
reader a general idea of the relative position of the 
planets, and may perhaps aid the mind in forming cor- 
rect conceptions. 

RELATIVE POSITION OF THE PLANETS. 




14 THE YOUNG ASTRONOMER. 



THE SOLAR SYSTEM. 
THE SUN. 



The Sun is the centre of the Solar system. For 
many ages that vast luminary was supposed to be a 
globe of liquid fire. But now the body of the Sun is 
ascertained to be a solid and dark mass, of stupendous 
magnitude ; somewhat resembling in its aspect the 
globe on which we live. A luminous atmosphere, 
many distinguished Astronomers have conjectured, of 
vast extent, and of intense brilliancy, surrounds the 
solid body of the Sun, and throws out its rays of light 
and heat to the most distant of the planetary worlds. 
In this atmosphere of dazzling splendor, there are 
frequently seen openings or cavities, through which is 
distinctly visible the dark mass of the interior globe. 
It is impossible to ascertain what is the precise nature 
of this luminous substance, of such intense energy, 
which envelopes the Sun. Many have supposed it to 
be analogous to the electric fluid which gleams from 
the thunder clouds ; and that vast accumulations of 
this subtle and inexplicable element surround the Sun. 
These electric clouds, or luminous vapors, are supposed, 
by Herschel, to be between two or three thousand 



What body is the centre of the Solar system ? What was the Sun 
formerly supposed to be ? What is the Sun now ascertained to be ? 
From whence does the light and heat of the Sun proceed ? What is 
frequently seen in this atmosphere ? What is the precise nature of this 
luminous substance ? To what have many supposed it to be analogous ? 
How thick are these luminous clouds ? 



THE SOLAR SYSTEM. 15 

miles in thickness. This discovery of modern science 
beautifully illustrates the Mosaic account of the crea- 
tion. It is there said that light was created before the 
Sun itself. This now appears reasonable. For light 
or this luminous atmosphere was first created. The Sun 
was then appointed the great light-bearer ', around which 
the luminous substance was gathered. Thus has the 
advancement of science removed a difficulty in the ac- 
count of the creation, which in the days of ignorance 
perplexed the mind. 

The cavities which are seen in these luminous clouds, 
appear like dark spots on the surface of the Sun. Some 
are found to be of the most enormous magnitude. The 
smallest which are visible to us, are not less than five 
hundred miles in diameter. Some have been ascer- 
tained to be more than forty thousand miles in length, 
and sixteen thousand in breadth. Upon such a spot 
as this, ten globes, as large as the earth, might be 
placed. These spots never continue for a long time of 
the same figure ; but are subject to numerous and ra- 
pid changes. It is seldom that any one spot continues 
for more than six weeks. The luminous clouds seem 
to close together, and as one spot disappears, others are 
seen in other places. Some occurrences seem to lead to 
the opinion that when there are many spots observed 



What does the discovery of these luminous clouds illustrate ? What 
difficulty has appeared in the Mosaic account of the creation ? How 
does this discovery remove the difficulty ? How do the cavities in these 
luminous clouds appear ? Are they large or small ? What is the size 
of the smallest ? What is the size of the largest ? What illustration is 
given of the size of this largest cavity ? How long do these spots gene- 
rally continue ? Describe the mode of their change ? What opinion has 
been drawn respecting the influence of these spots upon temperature ? 



16 THE YOUNG ASTRONOMER. 

on the surface of the Sun, the heat of the Snn is dimin- 
ished. But upon this subject not enough facts have 
yet been collected to lead to any positive conclusion. 

Beneath this atmosphere of such ineffable splendor, 
and between it and the sun, there is observed to be a 
second atmosphere, or stratum of clouds, of inferior 
brightness. It is supposed that this cloudy stratum is 
intended as a screen, to protect the inhabitants of the 
Sun from the too excessive light and heat of the elec- 
tric or luminous atmosphere which surrounds that stu- 
pendous globe. Thus there may be a happy popula- 
tion rejoicing in the valleys and along the hillsides of 
that magnificent mansion of our God. They may en- 
joy the luxury of an ever genial clime. They may 
dwell in attempered rays of heat and light, which never 
dazzle and never burn. 

The magnitude of the Sun surpasses all powers of 
human conception. The Sun is about nine hundred 
thousand miles in diameter. It is three millions of 
miles in circumference. But these vast numbers con- 
vey no distinct conception to the human mind. The 
imagination may, perhaps, be slightly aided by the 
following illustrations of the Sun's magnitude. 

1. Were the Sun placed where the Earth now is, its 
solid contents would fill the whole space enclosed by 
the orbit of the Moon ; and it would extend two hun- 



Why is there no positive conclusion upon this subject ? What is in- 
terposed between these luminous clouds and the surface of the Sun ? 
What is supposed to be the object of this screen ? What inference is 
drawn from this fact ? What is the diameter of the Sun ? Do these 
numbers convey any distinct idea to the mind ? How may the imagi- 
nation be aided ? What is the first illustration of the magnitude of 
the Sun ? 



THE SOLAR SYSTEM, 17 

dred thousand miles in every direction beyond the orbit 
of the Moon. The whole of this almost measureless 
region would be filled with the solid contents of that 
stupendous orb. 

2. Were a person to travel over thirty square miles 
of the Sun every day, it would require more than two 
hundred and twenty millions of years to survey its sur- 
face. 

3. Were the Sun a hollow ball, it would contain 
thirteen hundred thousand globes as large as the Earth. 

4. If the surface of the Sun were peopled with in- 
habitants, it would sustain as large a population as could 
live on eight hundred and fifty thousand such globes 
as the Earth. 

Notwithstanding these illustrations, the mind in vain 
endeavors to attain a conception of the grandeur of this 
majestic globe. Even angelic powers may be exhausted 
in the endeavor to grasp the grand idea. It is consid- 
ered as a demonstrated truth, that the surface of the 
Sun is diversified with towering mountains and wide- 
spread vales. And upon these hillsides and verdant 
savannahs, where no night ever darkens the sky, and 
no winter ever chills the flowers or the fruit, there may 
be beauty and luxuriance of vegetation, such as Eden 
never witnessed. There is probably no night upon 
the Sun, for it is enveloped, at all times, in a blaze of 
splendor. There is probably no winter upon the Sun, 
for that atmosphere, which is the fountain of heat, 



What is the second illustration of the magnitude of the Sun ? What 
the third ? What the fourth ? How is the surface of the Sun diversi- 
fied ? Is there any night upon the Sun ? Why not ? Is there any win- 
ter there ? Why not ? 



18 THE YOUNG ASTRONOMER. 

exists equally at the equator and at the poles. May 
we not hope that a sinless population crowds those 
blissful vales. If there the clamor of selfishness and 
of oppression is unknown, and every heart throbs with 
love for God, and love for its fellow, surely this realm, 
in all its amplitude, is worthy to be ranked among those 
heavenly mansions, which our Saviour has gone to 
prepare for his followers. As one star differeth from 
another star in glory, and as there are different degrees 
of rank and elevation among the intelligences whom 
God has formed, it is by no means improbable that the 
Sun may be peopled by a loftier race than man ; by a 
race unsusceptible of fatigue, and living in the vigor 
of eternal youth. It is one of the peculiarities of the 
future home of redeemed man, that " there is no night 
there." 

The Sun has a revolution upon its own axis. It re- 
volves once in about twenty-five days. This rotation 
was discovered by the motion of spots on the surface 
or disk of the Sun. A dark spot will frequently ap- 
pear on the eastern edge of the Sun, and move gradu- 
ally along, day after day, till it arrives at the western 
edge. Then disappearing, in the course of about 
twelve days it will again be seen manifesting itself 
upon the eastern edge. The regular rotation of these 
spots, proves that the Sun is a globe ; and that it re- 
volves upon its own axis from east to west, in about 



What pleasing hope may we indulge ? What supposition is not im- 
probable ? What motion has the Sun ? In what time does the Sun re- 
volve upon its axis ? How was this rotation discovered ? Describe the 
movement of these spots ? . What does the regular rotation of these 
spots prove ? 



THE SOLAR SYSTEM, 19 

twenty-five days. The Sun is eclipsed when the Moon, 
passing between the Earth and the Sun, casts its shadow 
on the Earth, as is seen in the accompanying diagram. 




Besides the revolution of the Sun upon its own axis, 
Herschel conjectures that the Sun, carrying with it all 
the planetary system, is circling around some distant 
and unknown centre. What that centre is no one can 
tell. In what depths of space it is buried, no one can 
imagine. But the idea is sublime in the highest de- 
gree, that the stupendous Sun itself, with all its retinue 
of revolving worlds, is gliding through the depths of 
space in an immeasurable orbit. Probably thousands 
of years are occupied, in traversing this limitless path- 
way. Herschel was led to this conjecture, by observ- 
ing that the stars, in one quarter of the heavens, appear 
to be very gradually approaching each other, while in 
an opposite quarter the stars as gradually seem to re- 
cede. This apparent motion, almost imperceptible as 
it is, would be caused by an actual movement of the 
Sun towards the stars, which seem to be receding from 
each other. 



When is the Sun eclipsed ? What motion has the Sun besides a re- 
volution upon its axis ? What is the centre around which the Sun 
revolves ? What length of time is probably occupied by the Sun in 
traversing its circuit ? What led Herschel to the conclusion that the 
Sun revolves around some distant centre ? What would cause the stars 
apparently to recede from each other ? 



20 THE YOUNG ASTRONOMER. 

The distance of the Sun from the Earth is estimated 
to be seventy-five millions of miles. A carriage, trav- 
eling at the rate of twenty miles an hour, would oc- 
cupy more than five hundred years in traversing this 
distance. Many persons are incredulous, respecting 
the ability of Astronomers to measure the vast distances 
interposed between the heavenly bodies and the Earth. 
But the principles upon which this measurement is 
conducted are perfectly simple, and the results demon- 
strably accurate. Any civil engineer can measure the 
height of a distant mountain, or a fortress, though he 
may not be able to climb the mountain, and the for- 
tress may be inaccessible. He simply measures a base 
line, upon the ground on which he stands. From the 
two extremities of this line, he takes the bearing of 
the object; that is the angle which a line running to 
the distant object makes with the base line. Then 
from the most simple principles of geometry and arith- 
metic, he calculates the distance of the object. It is in 
this way that most of the surveys on Earth are taken. 
Neither the magnitude nor the distance of the object 
under observation increases the difficulty of the mea- 
surement. 

In measuring the distance of the heavenly bodies, 
we take for a base line the diameter of the Earth, 
which is eight thousand miles. And when the distance 



What is the distance of the Sun from the Earth ? How long would 
it take a carriage to traverse this distance at the rate of twenty miles 
an hour ? What is said of the accuracy of astronomical measurements ? 
How does a civil engineer measure heights which are inaccessible ? 
What does not add to the difficulty of measurement ? In measuring the 
distance of heavenly bodies what is taken as the base line ? What is 
the diameter of the Earth ? 



THE SOLAR SYSTEM. 21 

of the object observed is such that even that vast line 
dwindles, as it were, into a point, we take for a base 
line the diameter of the Earth's orbit. This line is 
nearly two hundred millions of miles in length. To 
pass over it, in a rail-car travelling at the rate of thirty 
miles an hour, would require nearly eight thousand 
years. The more distant the object is, the larger, of 
course, is the angle of its bearing with the base line. 
If the object be so distant that there is no perceptible 
angle at all, of its bearing with the base line, the dis- 
tance of the object cannot be measured. Under such 
circumstances, it is certain that the object cannot be 
within certain limits, but its positive distance cannot be 
ascertained. And such is the fact in reference to nearly 
all the stars glittering in the firmament. With so stu- 
pendous a base line as the diameter of the Earth's or- 
bit, no perceptible change in their bearing can be per- 
ceived from either extremity. 

The Earth is farther from the Sun when in one part 
of its orbit than when in another part. This results 
from the fact that the orbit in which the Earth revolves 
is not a perfect circle. Its diameter in one direction is 
more than three millions of miles longer than in the 



When the diameter of the Earth is not sufficient what is taken ? What 
is the length of the diameter of the Earth's orbit ? How long would it 
take a carriage, at the rate of thirty miles an hour, to pass over this 
line ? What influence has the distance of an object upon the angle of its 
bearing with a base line ? When can the distance of an object not be 
measured ? What is certain in such a case ? What is the fact in refer- 
ence to the fixed stars generally ? With what base line is it endeavored 
to measure their distance ? Is the Earth always equally distant from 
the Sun ? Why is it not always equally near the Sun ? How much dif- 
ference is there in the diameters of its orbits ? 



22 THE YOUNG ASTRONOMER. 

other. Such a figure is called an ellipse. The differ- 
ence between the longest and the shortest diameter is 
called the eccentricity of the ellipse. The Earth is 
nearest the Sun in winter, and farthest from it in sum- 
mer. In summer, however, the rays of the Sun fall 
nearly perpendicularly upon us, causing intense heat. 
In the winter the rays fall upon us obliquely, and 
hence the severity of the cold. 

Almost every motion which takes place on the sur- 
face of the Earth is influenced by the rays of the Sun. 

1. All winds are caused by the heat of the Sun pro- 
moting currents of air in the atmosphere. Particles of 
air heated intensely in one place by the rays of the 
Sun, rapidly rise, while the surrounding atmosphere 
rushes in to fill the vacant space. Hence gentle 
zephyrs, tornadoes and whirlwinds. 

2. The whole vegetable kingdom is dependent for 
life and growth upon the light and heat of the Sun's 
rays. 

3. The heat of the Sun raises, by evaporation, the 
water of the ocean, circulates it in vapor over the land, 
and then letting it fall in showers, creates all the 
springs and rivers. 

4. The crumbling of the mountains even is caused 
by the abrasion of the wind and rain, and the change 
of the seasons which the Sun produces. 

What is such a figure called ? What is meant by the eccentricity of 
an ellipse ? When is the Earth nearest the Sun ? When farthest from 
it ? Why have we intense heat in summer ? Why cold in winter ? By 
what are most of the motions which take place on the surface of the 
Earth influenced ? How are winds caused ? How does the heat of the 
Sun promote currents in the atmosphere ? Upon what does the vege- 
table kingdom depend ? How are springs and rivers caused ? How is 
the crumbling of mountains caused. 



THE SOLAR SYSTEM. 23 

It has long been a question of much interest, whether 
the Sun is probably inhabited. Upon this question 
Astronomers are not yet fully agreed. The following 
arguments have been adduced by the most eminent 
Astronomers, in favor of the Sun being peopled. They 
are sufficient to lead most minds to the conclusion that 
probably countless myriads of happy beings are rejoic- 
ing amid the splendor of that vast orb. 

1. The Sun is evidently a solid globe of mountains 
and valleys, and thus adapted to be the home of intel- 
ligent creatures. 

2. It is contrary to analogy to suppose that God, 
who fills every drop of water with animal life, would 
create so magnificent and beautiful a world, and leave 
it to solitude and desolation. 

3. There is evidence that beneath the luminous 
clouds which surround the Sun, there is an inner at- 
mosphere, which seems to be carefully prepared as a 
veil, to screen the inhabitants of the Sun from too ex- 
cessive heat. 



Is the Sun probably inhabited ? What is the first argument in favor 
of its being inhabited ? What the second ? What the third ? 



24 THE YOUNG ASTRONOMER. 



CHAPTER II. 



THE PLANETS— MERCURY— VENUS— THE 
EARTH. 

All those solid celestial bodies resembling the Earth, 
which revolve around the Sun, are called planets. 
The planets are divided into two classes. They 
are the primary and the secondary. The primary 
planets are those which revolve around the Sun as a 
centre. There are twelve of them now discovered. 
They are named Mercury, Venus, the Earth, Mars, 
Vesta, Astrea, Juno, Ceres, Pallas, Jupiter, Saturn, 
and Herschel. The primary planets are also divided 
into superior and inferior. The superior planets are 
those which are more remote from the Sun than the 
Earth is. There are nine of them : they are Mars, 
Vesta, Astrea, Juno, Ceres, Pallas, Jupiter, Saturn 
and Herschel. The inferior planets are those which are 
nearer the Sun than the Earth is. There are two of 
them : they are Venus and Mercury. 



What are planets ? Into how many classes are planets divided ? 
What are the two classes ? What are the primary planets ? How 
many primary planets are there ? Name them. Into what classes 
are the primary planets divided ? What are the superior planets ? 
How many superior planets are there ? Name them. What are the 
inferior planets ? How many are there ? Name them. 



MERCURY. 25 

The secondary planets are those which revolve 
around a primary planet as a centre. There are 
eighteen secondary planets : they are the Earth's 
moon, the four moons of Jupiter, the seven moons of 
Saturn, and the six moons of Herschel. Thus there 
are thirty planets now known as belonging to the 
solar system. There may be others, also, which have 
not as yet been discovered. 

MERCURY. 

The planet Mercury is nearer to the Sun than any 
other which has yet been discovered. This planet 
revolves in an orbit distant about thirty-seven millions 
of miles from the Sun. It is seldom visible, for it is so 
near the Sun that it is usually hidden in the Sun's rays. 
Mercury is small compared with the Earth. The 
Earth is sixteen times larger than Mercury. It is, 
however, estimated that Mercury could sustain a much 
larger population than has ever lived, at any one time, 
upon the Earth. But a very small portion of the 
Earth has ever been thickly populated. If the planet 
Mercury were inhabited as densely as is the island of 
Great Britain, it would support more than eleven 
times the present population of this globe. Mercury 



What are secondary planets ? How many secondary planets are 
there ? Name them. How many planets belong to the Solar System ? 
Is it certain that there are no more ? What planet is nearest to the 
Sun ? How far is Mercury from the Sun ? Is it often seen ? Why 
is it seldom seen ? How much larger is the Earth than Mercury ? 
What is said of the probable population which Mercury could sustain ? 
How large a portion of the Earth has ever been thickly inhabited ? 
How large a population would Mercury support ? 
2 



26 THE YOUNG ASTRONOMER. 

performs a revolution around the Sun in about three 
months, moving with the vast velocity of about one 
hundred thousand miles an hour. No other planet 
revolves with so swift a motion. A year on the planet 
Mercury is of course equal to but three of our months. 
As Mercury revolves upon its own axis once in about 
twenty-four hours, a day upon that planet must be of 
about the same duration as a day with us. Mountains 
have been seen, by an eminent German astronomer, 
upon the surface of that planet, and two of them have 
been measured. The most lofty was found to be 
about ten miles in height. It is also ascertained that 
Mercury is surrounded by an exceedingly dense atmo- 
sphere. This may perhaps be prepared of such a na- 
ture as to screen its inhabitants from the too excessive 
light and heat of the Sun. It is impossible to ascer- 
tain whether Mercury has any attendant moon, for a 
body so small could not be seen immersed in the Sun's 
rays. In fact, Mercury is very rarely seen, even with 
the telescope ; it has, however, occasionally been seen 
with the naked eye. 

Notwithstanding the comparative smallness of the 
planet, it is altogether probable that, in the grandeur 

In what time does Mercury revolve around the Sun ? With what 
speed does Mercury revolve in its orbit ? Does any other planet re- 
volve as swiftly ? How long is a year on Mercury ? In what time 
does Mercury revolve upon its axis ? How long is a day upon Mer- 
cury ? What is said of the discoveries of an eminent German Astron- 
omer ? How high is the loftiest mountain upon Mercury ? What 
is said of the atmosphere of Mercury ? What may be the object of so 
dense an atmosphere ? Has Mercury any moon r Why could not a 
moon of Mercury be seen ? Is Mercury often seen with the tele- 
scope ? Has it ever been seen with the naked eye ? What is said to 
be probable, notwithstanding the smallness of the planet ? 



VENUS. 27 

of scenery, and in the moral elevation and intellectual 
dignity of its inhabitants, it holds a far more distin- 
guished rank under the government of God than the 
world we inhabit. 

VENUS. 

Venus is the most beautiful of all the planets. This 
planet revolves in an orbit about seventy millions of 
miles from the Sun. When in one part of its orbit, it 
rises just before the Sun, and is then called the morn- 
ing star ; when in the opposite part of its orbit, it sets 
soon after the Sun, and it is then called the evening 
star. Venus is of about the same size as the Earth. It 
revolves upon its axis (thus producing day and night) 
once in twenty-four hours. Its annual revolution 
about the Sun is performed in about seven months. 
Thus, a year upon the planet Venus is equal to but 
little more than half a year on this globe. The 
surface of Venus is diversified with mountains and 
valleys. Many of these mountains are far more lofty 
than any which are beheld on the Earth. One moun- 
tain is visible which is estimated to be more than 
twenty miles in height. The highest on the Earth 
are not more than five miles in height ; consequently, 



Which is the most beautiful of the planets ? What is the distance 
of Venus from the Sun ? When is Venus called the morning star ? 
When is it called the evening star ? What is the size of Venus ? In 
what time does it revolve upon its axis ? In what time does it re- 
volve about the Sun ? How long is a year upon Venus ? What is 
said of the surface of Venus ? What is said of the height of many of 
these mountains ? How high is one estimated to be ? How high are 
the highest on Earth ? 



28 THE YOUNG ASTRONOMER. 

the scenery upon Venus must be far more sublime 
than any which we witness. Clouds creep up the 
sides of these majestic mountains, and float in the 
atmosphere with which the planet is enveloped. 
Apparently, there are no very large bodies of water, 
like our oceans, upon the planet Venus. The clouds, 
however, floating in the atmosphere, indicate that the 
planet is supplied with lakes and rivers. To an inhab- 
itant of Venus, the Sun appears twice as large as it 
does to us, and the planet Mercury is her morn- 
ing and evening star. When the Earth and Venus 
are in a particular position, Venus may be seen, 
appearing like a black ball, passing over the surface 
of the Sun. This phenomenon is called a transit of 
Venus. These transits are of very rare occurrence. 
It is uncertain whether Venus has any satellite, or 
moon. If Venus have a satellite, it must, in conse- 
quence of its distance, and its proximity to the Sun, 
be very difficult to be seen. Many astronomers, how- 
ever, think that, in certain favorable positions, they 
have discovered a moon revolving around Venus, of 
about the same size as our moon. It is estimated that 
Venus would sustain a population more than sixty- 
seven times the present population of the Earth ; con- 
sequently, it may be in rank a world of far greater 
importance than our own. 

What is said of the scenery upon Venus ? What is said of clouds 
on the planet Venus ? Are there large bodies of water on Venus ? 
What do the clouds indicate ? How large does the Sun appear to an 
inhabitant of Venus ? What is the morning and evening star to an 
inhabitant of Venus ? What is a transit of Venus ? Has Venus any 
moon ? Why cannot her moon, if she have any, be easily seen ? 
W 7 hat do many astronomers think ? What population would Venus 
sustain ? 



THE EARTH. 29 



THE EARTH. 

The third body in the solar system is the Earth. 
The form of the Earth is that of a globe, a little flat- 
tened at the two ends, like an orange. Such a figure 
is called an oblate spheroid. The diameter of the 
globe, from east to west, is about thirty-four miles 
longer than from north to south. The Earth is eight 
thousand miles in diameter, and twenty-five thousand 
miles in circumference. The atmosphere which sur- 
rounds the globe, is about forty miles in thickness 
The Earth revolves in an orbit, at the distance of nine 
ty-five millions of miles from the Sun ; and rushing 
along its pathway, with the velocity of a thousand 
miles a minute, it performs its annual revolution in 
three hundred and sixty-five days, six hours, nine 
minutes and twelve seconds. It is, indeed, a sublime 
idea, that the world in which we dwell is thus career- 
ing onward, through the. depth of space, with such 
fearful velocity. We pass through sixty thousand 
miles of space every hour. 

Though the Earth is not a perfect globe, yet it is so 
nearly so, that if a perfect model of the Earth were 
made, the eye could not detect that it was not perfect- 

What is the third body in the Solar System ? What is the form of 
the Earth ? What is such a figure called ? What difference is there 
in the diameter of the Earth ? Which diameter is the longest ? What 
is the length of the Earth's diameter ? What is its circumference ? 
What is the thickness of the Earth's atmosphere ? What is the dis- 
tance of the Earth from the Sun ? With what velocity does it re- 
volve ? In what time does it perform its annual revolution ? What 
space do we pass through each hour ? How nearly a perfect globe is 
the Earth ? 



30 



THE YOUNG ASTRONOMER. 



ly round. There are various and conclusive proofs, 
that the Earth is of a globular form. 

1. It has been sailed around. 

2. A ship receding from the shore exhibits the tops 
of the masts, as is illustrated in the diagram, when the 
body of the ship is below the horizon. 



3. The shadow which the Earth casts upon the Moon 
in an eclipse, is precisely that which one globe would 
project upon another globe. 

Some may suppose that the Earth cannot be consid- 
ered as globular, in consequence of the lofty ridges of 
mountains upon its surface. But the inequality caused 
by the mountains, is not at all incompatible with the 
idea of its spherical form. The highest mountains on 
the Earth are not more than five miles in height. 
The diameter of the Earth is eight thousand miles ; 
consequently, the proportion of the highest pinnacle of 
the loftiest mountain to the diameter of the globe, is 
but as five to eight thousand, or one to sixteen hun- 



What is the first proof that the Earth is round ? What the second ? 
What the third ? Why do some think that the Earth cannot be consid- 
ered globular ? What is said of this inequality ? How high are the 
highest mountains ? What is the proportion of these mountains to 
the diameter of the globe ? 



THE EARTH. 31 

dred. The surface of the Earth, in consequence of 
its mountainous inequalities, has sometimes been com- 
pared with the roughness on the rind of an orange. 
But this illustration assigns altogether too great a com- 
parative elevation to the height of the mountains. If 
you take a globe sixteen inches in diameter, and paste 
upon it a strip of the thinnest paper, the thickness of 
that paper would represent the loftiest range of moun- 
tains on the Earth. Such is the comparative height 
of the inaccessible pinnacles of Mt. Blanc. When we 
think of men, thronging such valleys, and toiling for 
weary days in the ascent of such acclivities, well may 
we inquire, in the language of the inspired penman, 
u What is man, that thou art mindful of him, and the 
son of man, that thou deignest to visit him?" 

It is also supposed that the ( greatest depth of the 
ocean does not exceed the height of the mountains ; 
consequently, on a sixteen-inch globe, the ocean 
would be represented by the thinnest film of water 
laid upon it with a brush. The slightest scratch of a 
pin would represent the Mississippi and the Amazon. 
These illustrations show that, notwithstanding our 
towering mountains and deep valleys, the Earth may 
be regarded as a true globe. 

As the orbit of the Earth is not exactly circular, 
the Earth is at certain seasons of the year about three 

To what has this inequality sometimes been compared ? Why is 
not this a good comparison ? What would be a correct representation 
of the loftiest mountains ? What is the greatest depth of the ocean 
supposed to be ? What would correctly represent the depths of the 
ocean ? What would represent the Mississippi and the Amazon ? 
What do these illustrations show ? Why is the Earth at one .time 
nearer the Sun than at others ? 



32 



THE YOUNG ASTRONOMER. 



millions of miles nearer the Sun than at other seasons. 
The Earth is nearest the Sun about the first day of 
January ; but as the rays of the Sun then fall obliquely 
upon the Earth, the cold is severe. The Earth is 
farthest from the Sun about the first of July. But as 
the rays of the Sun then fall nearly perpendicularly 
upon us, the heat is oppressive. The diagram illus- 
trates this principle. About the 21st day of March 




and the 23d of September, the Sun crosses the 
equator, and the days and nights are then equal in 
length in all places. These periods are called the 
equinoxes, from two Latin words, signifying equal 
nights. When the Sun passes the equator in March, 
it is called the vernal equinox. When it passes the 



How much nearer is it at one season than at another ? When is the 
Earth nearest the Sun ? Why is it then so cold ? When is the 
Earth farthest from the Sun ? Why is it then so warm ? When 
does the Sun cross the equator ? What is the comparative length of 
the days and nights then ? What are those periods called when the 
days and nights are equal ? What is the vernal equinox ? 



THE EARTH. 



33 



equator in September, it is called the autumnal equi- 
nox. The time between the vernal and autumnal 
equinox is about eight days longer than the time be- 
tween the autumnal and the vernal equinox. 

The shortest day and the longest night north of the 
equator are on the 21st of December. This time is 
called the winter solstice. It is so called from two 
Latin words, signifying that the Sun stands or stops. 
At that time, the Sun apparently ceases going any 
farther south, and returns again towards the north. 
Crossing the equator, it arrives at its extreme northern 
limits on the 21st of June. At this time we have the 
longest day and the shortest night, and this is called 
the summer solstice. 




Nearly three-quarters of the surface of the Earth is 
covered with water. The present population of the 



What is the autumnal equinox ? Between which of the equinoxes 
is there the longest time ? How much the longest ? When is the 
shortest day ? What is this period called ? From what is this name 
derived ? What change is there then in the apparent movement of 
the Sun ? When does the Sun arrive at its extreme northern limit ? 
What is the comparative length of the day at that time ? What is 
that period called ? What portion of the Earth's surface is covered 
with water ? What is the present population of the globe ? 



34 THE YOUNG ASTRONOMER. 

globe is estimated to be about one thousand millions. 
Were all the habitable portions of the globe peopled 
as densely as England, the Earth would sustain nearly 
twenty times its present population. But war, the 
greatest scourge which has ever afflicted humanity, 
has thus far so thinned out the number of the human 
family, that but about one-seventeenth of the habit- 
able globe is yet peopled. If it were not for past wars 
and the vices of mankind, every habitable portion of 
the globe would be smiling with cultivated fields and 
peaceful villages. And the spirit of war, which even 
now is cherished, in sustaining expensive armies and 
navies, is one of the most serious obstacles which now 
exist in the way of human improvement. 

It is often necessary to ascertain the particular posi- 
tion of a place upon the Earth's surface. To do this, 
it is necessary to settle some fixed points or lines to 
which we may refer various places. One of these 
lines is the equator, which is an imaginary line, pass- 
ing around the centre of the Earth, from east to west. 
The poles are those points, equally distant from the 
equator, where the axis of its diurnal revolution ter- 
minates. These are called the north and south poles. 
The hemispheres, or half-spheres, into which the 
equator divides the globe, are called the northern 
and southern hemispheres. The distance of any place 

What population could this Earth sustain ? What has been the 
effect of war ? What would have been now the case if wars and 
other vices had not prevailed ? What is the influence of the present 
war-spirit? What is first necessary to ascertain the position of a 
place upon the Earth's surface ? What is the equator ? What are 
the poles ? What are the poles called ? What are the two hemi- 
spheres into which the equator divides the Earth called ? What is 
Latitude ? * 



THE EARTH. 35 

from the equator is called its latitude, and latitude is 
consequently reckoned in the direction of north and 
south, and a place is said to be in northern and south- 
ern latitude as the place is in the northern or southern 
hemisphere. But while the latitude will determine 
how far a place is north or south of the equator, it 
does not indicate its position east or west of any given 
place, for the line of latitude of course encircles the 
globe. The distance of a place east or west of any 
assumed point is called longitude. To ascertain the 
longitude of a place, the earth is supposed to be en- 
circled by a line, dividing it into two equal parts, 
passing through some place which is assumed as the 
point from which to measure the longitude. Wash- 
ington has sometimes been assumed. Philadelphia 
has also been selected as the point from which longi- 
tude is reckoned. In England, the Royal Observatory 
is erected at Greenwich, a short distance from Lon- 
don ; consequently, in all English w T orks, longitude 
is reckoned from the meridian of Greenwich. These, 
then, are the standards of reference from which to de- 
cide the position of any place on the surface of the 
globe. When it is said that the city of New York is 
situated in about 41 degrees north latitude, and about 
75 degrees west longitude, it is meant that the city is 
41 degrees north of the equator, and 75 degrees west 

When is a place said to be in North Latitude ? When in South 
Latitude ? What is Longitude ? To ascertain the Longitude of a 
place, what is supposed ? What places in America have been as- 
sumed as the points from which Longitude is reckoned ? Where is 
the Royal Observatory in England ? From what place is Longitude 
reckoned in English works ? What is meant by the assertion that the 
City of New York is in 41 Q North Lat. and 75° West Long. ? 



36 THE YOUNG ASTRONOMER. 

of the meridianal line which passes over the Observa- 
tory of Greenwich. 

The process by which the latitude of any place, 
either on the land or sea, is discovered, is very simple. 
A circle is divided into three hundred and sixty de- 
grees. From the equator to either pole is a quarter of 
a circle, or ninety degrees. By a very simple instru- 
ment, the point in the sky directly overhead, which 
is called the zenith, is ascertained. By observation, 
the distance of that point from the north pole is deter- 
mined. Suppose this distance to be sixty degrees, 
that number subtracted from ninety degrees, which is 
a quarter of a circle, will designate the precise dis- 
tance of the place from the equator. An instrument 
called Hadley's Sextant is generally used at sea for 
making such observations. 

There is another mode of ascertaining the latitude, 
which is, however, essentially the same in principle. 
The distance of the Sun from the equator is called its 
declination. The declination of the Sun is known, 
and registered in tables for every day in the year. By 
ascertaining, by observation, the distance of the Sun 
from the zenith, and adding that distance to the Sun's 
declination, the latitude of the place is determined. 

To find the longitude of a place by observation, is 
much more difficult, as there are no visible fixed points 

Into how many degrees is a circle divided ? How many degrees is 
it from the equator to either pole ? What is the point in the sky di- 
rectly overhead called ? Describe the first mode of ascertaining the 
Latitude. What instrument is generally used ? What is the distance 
of the Sun from the equator called ? Describe the second mode of 
ascertaining the Latitude. Why is it more difficult to ascertain the 
Longitude ? 



THE EARTH. 37 

from which to calculate. The usual mode is the fol- 
lowing. The Sun appears to pass around the globe 
in about twenty-four hours ; and as the circumference 
of the globe, and of every circle, is divided into three 
hundred and sixty degrees, the sun passes over fifteen 
degrees in one hour. Consequently, when it is twelve 
o'clock in Greenwich, fifteen degrees west of Green- 
wich it will be eleven o'clock, and thirty degrees 
west it will be ten o'clock, and forty-five degrees west 
it will be nine o'clock. By this simple principle, longi- 
tude is usually calculated. The mariner takes with 
him a watch or time-keeper of the most perfect con- 
struction, called a chronometer. This is set according 
to the time at Greenwich ; and, consequently, will in- 
form him, wherever he may be, what o'clock it is at 
the Royal Observatory. At noon he takes an obser- 
vation, when the sun is in the meridian, and thus 
ascertains that it is twelve o'clock. He looks at his 
chronometer, and finds that at that moment it is one 
o'clock at Greenwich. He thus knows that it will re- 
quire the Sun just one hour to move, in its apparent 
orbit, from Greenwich to where he is ; and as the 
Sun's apparent motion is fifteen degrees an hour, he 
knows that he is in the longitude of fifteen degrees 
west of Greenwich. Such are the general principles 
on which latitude and longitude are calculated. It is 
not necessary to explain here the corrections necessary 
in the practical workings of these methods. 



Over how many degrees does the Sun appear to pass in one hour ? 
When it is 12 o'clock in Greenwich, what time will it be 15° West of 
Greenwich ? What time 30° West ? What time 45° West ? What is 
a chronometer ? Describe the first mode of ascertaining the Longitude. 



38 THE YOUNG ASTRONOMER. 

There is another mode of ascertaining the longitude 
of a place, by what is called a lunar observation. It 
has been thus eloquently described by Dr. Lardner : 
u The astronomer supplies the mariner with a chro- 
nometer of unerring precision ; a chronometer which 
can never go down nor fall into disrepair ; a chrono- 
meter which is exempt from the accidents of the deep ; 
which is undisturbed by the agitation of the vessel ; 
which will at all times be present and available to him, 
wherever he may wander over the trackless and unex- 
plored regions of the ocean. Such a chronometer has 
been found, made by an artist who cannot err, and 
into whose works imperfection can never enter. Such 
a chronometer is supplied by the firmament itself. 
The unwearied labors of modern astronomers have 
converted the face of the heavens into a clock, and 
have taught the mariner to read its complicated but 
infallible indications. We may regard, for this pur- 
pose, the firmament as a dial-plate of a chronometer, 
on an immense scale. The constellations and the 
fixed stars upon it, which for countless ages are sub- 
ject to no change in position, serve as the hour and 
minute marks. The Sun, the Moon, the planets and 
the satellites, which move continually over the surface 
of this splendid piece of mechanism, play the parts of 
the hands of the clock. The position of these bodies 
from day to day, and from hour to hour, and every 
change of their position, are accurately foreknown, 
and exactly registered in a book published some 



What is the second mode of ascertaining the Longitude called ? 
Give the substance of Dr. Lardner's description. Describe the 
second mode of ascertaining the Longitude. 



THE EARTH. 39 

two or three years in advance, called the c Nautical 
Almanac,' and circulated for the benefit of mariners. 
In this work, the navigator is told what the hour is, 
or will be, at Greenwich, for every variety of position 
which the Sun, Moon and planets shall have, from 
time to time, upon the heavens. But of all the ob- 
jects in the heavens, that which is best suited for this 
species of observation is the Moon. And hence, this 
method of determining the longitude at sea has been 
distinguished by the appellation of the lunar method." 
The mariner, with the sextant, observes the distance 
of the Moon from the Sun. The Nautical Almanac 
informs him what o'clock it is at Greenwich when the 
Moon is in that position ; and knowing the hour 
where he is, he easily calculates his distance from 
Greenwich. 



40 



THE YOUNG ASTRONOMER. 



CHAPTER III, 



THE MOON— MARS. 




A Moon, or satellite, is a 
planetary body which revolves 
around a primary planet as its 
centre. It is sometimes called 
a secondary planet. In an or- 
bit, distant about two hundred 
and forty thousand miles from 
the Earth, our Moon revolves. 

Telescopic View of the Moon. Though the Moon ig the nea rest 

to us of all the celestial bodies, it would require nearly 
a year and a half to journey to it, travelling day and 
night, at the rate of twenty miles an hour. 

The Moon is about two thousand miles in diameter. 
It is in bulk equal to but about one fiftieth part of the 
Earth ; and still, if it were inhabited as densely as 
the island of Great Britain now is, it would sustain 



What is a Moon or satellite ? What is it sometimes called ? At 
what distance from its primary does the Earth's Moon revolve ? What 
celestial body is nearest to the Earth ? How long would it take to 
reach the Moon, travelling at the rate of twenty miles an hour ? How 
long is the diameter of the Moon ? What is its size compared with 
the Earth ? How large a population could it sustain ? 



THE MOON. 41 

five times as many inhabitants as dwell at the present 
time upon the Earth. The Moon revolves upon its 
axis once in about twenty-eight days. Consequently 
a day and night upon the Moon is equal in length to 
a month on the Earth. The Moon performs a revo- 
lution upon its axis in the same time in which it re- 
volves around the Earth. It therefore always turns 
the same face to us. We never see but one and the 
same hemisphere of the Moon. The inhabitants who 
live upon the hemisphere turned from us, never see 
the Earth. As the Moon accompanies our Earth in 
its circuit around the Sun, it performs its revolution 
around that luminary in the same period of time with 
the Earth. While, therefore, a year on the Moon is 
as long as a year with us, it takes but twelve lunar days, 
each a month in length, to compose a lunar year. 

The surface of the Moon is diversified with moun- 
tains and valleys. The mountains and caverns which 
exist upon the Moon are thrown together in the most 
sublime disorder. The height of great numbers of 
these mountains has been accurately measured. Many 
of them are ranges several hundred miles in extent, 
and rising from two to five miles in height. 

There are large circular cavities or caverns existing 
on the face of the Moon, constituting a feature in lunar 



In what time does the Moon revolve upon its axis ? What is the 
length of a day and night upon the Moon ? Why does the Moon al- 
ways turn the same face to us ? In what time does the Moon perform 
its circuit around the Sun ? How long is a year on the Moon ? How 
long is a day ? How many lunar days are there in a year ? What is 
said of the surface of the Moon ? What is the size of the mountain 
ranges ? 



42 THE YOUNG ASTRONOMER. 

scenery, totally dissimilar from anything which is seen 
on Earth. These cavities are nearly circular in form, 
and their dimensions vary from three miles to fifty 
miles in diameter at the top, and some of them are 
three and a half miles in perpendicular depth. Many 
Astronomers have declared that with powerful tele- 
scopes, they h&ve witnessed volcanoes on the Moon, 
throwing out volumes of flame and smoke. Others, 
who have observed the same luminous appearances, 
have considered them either as lights of a phosphoric 
nature, or some artificial illumination of the inhabit- 
ants, rather than the eruption of volcanic fires. 

It has often been asserted that there is no water upon 
the Moon. There is, however, not sufficient evidence 
for so sweeping an assertion. It is admitted, however, 
by all Astronomers, that upon that half of the Moon 
which is visible to us, there are no large oceans or seas. 
There may, however, be rivers and small lakes, which 
the telescope does not bring to view. And there may 
be large oceans rolling upon that hemisphere which is 
ever secluded from earthly eyes. 

The question whether the Moon has an atmosphere, 
has also for a long time been disputed. Many Astro- 
nomers are now of the opinion, that the Moon has an 
atmosphere. No clouds are, however, ever detected 



What peculiar scene is witnessed in lunar scenery? What is the 
form of the lunar cavities ? What their extent ? What is said re- 
specting volcanoes in the Moon ? What assertion has been made re- 
specting water in the Moon ? Is it certain that there is no water 
there ? What is admitted by all Astronomers ? What may exist upon 
the Moon though unseen by us ? What is said respecting the Moon's 
atmosphere ? What is the present general opinion ? What is said re- 
specting clouds in the Moon's atmosphere ? 



THE MOON. 43 

in that atmosphere, to darken its serene sky. The 
Moon is eclipsed when the Earth, passing between the 
Sun and the Moon, casts its shadow upon that satellite, 
as is exhibited in the accompanying cut. In the an- 




nular eclipse of 1836, a distinguished observer says, 
" just before the rims of the two bodies met, the light 
of the Sun shot through the Moon's atmosphere molli- 
fied into lovely twilight." Lardner says, " it may be 
considered as demonstrated that the Moon has no at- 
mosphere." Schrceter, a very eminent Astronomer, 
who has passed years in examining the Moon with the 
most powerful glasses, says, that he has ascertained 
with absolute certainty that the Moon has an atmo- 
sphere. 

There has long existed an almost universal impres- 
sion, that the changes of the weather are influenced 
by the changes of the Moon. If the weather be fair or 
foul, it is supposed that at the period of new or full 
Moon, or at the epochs of the quarters, there will be a 
change. This almost universal impression is, how- 
ever, totally without foundation. There are no prin- 
ciples of science upon which to base such a theory. 



When is the Moon eclipsed ? What is Lardner's opinion ? What 
13 Schrceter's ? What impression respecting the influence of the Moon 
has long existed ? At what period is it supposed that a change of 
weather will take place ? Doe3 the Moon have any perceptible in- 
fluence on the weather ? 



44 THE YOUNG ASTRONOMER. 

The question of fact has also been settled by long and 
careful observation. Registers of the weather have 
been kept, in Europe, for long periods of time ; every 
change being noticed and registered, from day to day, 
and for years, with the utmost minuteness. And 
these changes have been carefully compared with the 
changes of the Moon. The result of this experiment, 
again and again repeated, has proved with absolute 
certainty, that the lunar phases have no perceptible 
influence whatever upon the weather. 

It is also a popular prejudice, that certain kinds of 
timber should be cut only during the decline of the 
Moon, or it will soon decay ; and also that trees should 
be planted, pruned, &c, only during the increase of 
the Moon. Accurate and long continued observation 
has proved that these notions have no support from 
facts. 

The deleterious influence of the Moon upon the in- 
sane has been considered so decisive, that he who is 
disordered in his mind is still called a lunatic, or one 
moon-struck. This opinion is also unsustained by any 
satisfactory evidence. Dr. Olbers, a distinguished 
physician and Astronomer, asserts that "in the course 
of a long medical practice, he was never able to dis- 
cover the slightest trace of any connection between the 
phenomena of disease and the phases of the Moon. 

It is the general opinion of Astronomers that the Moon 
is inhabited. Though we cannot hope by any increase 



How is this proved ? What is the popular impression respecting 
the influence of the Moon upon timber ? Why is an insane man called 
a lunatic ? What is the testimony of Dr. Olbers ? Is the Moon sup- 
posed to be inhabited ? 



THE MOON. 45 

of telescopic power, within the limits of probability, to 
see inhabitants on the Moon, it is not unreasonable to 
suppose that their works may be seen. In order to 
discern an object on the Moon as small as a man, a 
telescope must be used which has a magnifying power 
of one hundred thousand times. But such a telescope 
has never yet been constructed. HerschePs large tele- 
scope, the largest ever constructed, possessed a magni- 
fying power of six thousand. This noble instrument 
was about forty feet in length, and five feet in diame- 
ter. A telescope whose magnifying power is twelve 
hundred, will enable us to discern objects on the Moon 
which are three hundred feet in diameter. As there 
are many glasses of this magnifying power, it is very 
possible that cities and other large works may be dis- 
covered. 

Professor Gruithausen, of Munich, declares that he 
has discovered, by his large telescope, cities, fortifica- 
tions, roads and other artificial works, erected by the 
inhabitants of the Moon. He has even proposed the 
plan of opening a telegraphic correspondence with the 
inhabitants of that world. He suggests the erection, 
upon the plains of Siberia, of a vast geometrical figure. 
He thinks that the inhabitants of the Moon, seeing this 
figure through their telescopes, might regard it as a 
signal, and thus be induced to erect a similar one in 
reply. 



What must be the magnifying power of a telescope to discern a 
man upon the Moon ? What was the magnifying power of Herschel's 
large telescope ? What was the length of this instrument ? How 
small an object can be seen on the Moon, with a telescope which will 
magnify twelve hundred times ? What does Professor Gruithausen de- 
clare ? What plan has he proposed ? 



46 THE YOUNG ASTRONOMER. 

When we reflect upon the magnitude of the Moon, 
and the vast population it is capable of sustaining, it 
does not seem probable that the Creator would erect 
such a world, and abandon it to solitude. 

The tides of the ocean are caused by the attraction 
of the Moon. As the Moon revolves around the Earth, 
it attracts the water, and it follows the path of the 
Moon in a vast wave, several feet in height, flowing 
into all the bays and rivers and inlets. As the Moon 
comes to the meridian about half an hour later each 
day, the tide is consequently each day later. The 
highest tide is not directly under the Moon, but ipllows 
its path an hour or two in the rear. But in addition 
to the tide which follows the Moon there is another 
tide upon the side of the globe directly opposite. It 
is difficult to explain the cause of this, so as to make 
it perfectly familiar to the reader who is not skilled in 
scientific studies. It cannot, however, perhaps, be ex- 
plained in language more perspicuous than that in 
which it is described in the Encyclopedia Americana. 
" If the Earth rested immovably upon a fixed support 
there would be a tide only on the side towards the 
Moon. But the great body of the Earth is just as free 
to move as a single particle of the ocean, and if suffered 
to yield to the Moon's attraction, would be carried just 
as fast. Hence, for the same reason that a particle of 



Why should we suppose that the Moon is inhabited ? By what are 
the tides caused ? How does the Moon create a tide ? How much later 
is the tide each day ? Why is it thus later ? When is the highest tide ? 
What other tide is there in addition to the one which follows the Moon ? 
Is this second tide easily explained ? From what book is an explana- 
tion taken ? If the Earth were immovable, how many tides would there 
be ? What is said respecting the freedom of the Earth to move ? 



MARS. 47 

water, on the side of the Earth towards the Moon, is 
drawn away from the centre, or has its downward ten- 
dency diminished, so the solid Earth itself is drawn 
away from the mass of waters, on the side of the Earth 
farthest from the Moon. It is the difference of attrac- 
tion, in both cases, between the surface and the centre 
which causes the lightness of the waters and the con- 
sequent elevation." The tides are highest when the 
Sun and Moon attract in concert. These are called 
spring tides. When the Sun and Moon are opposite, 
and counteract each other, the tides are lowest. These 
are called neap tides. 

MARS. 

The next planet in the Solar system, as we leave 
the Earth and its accompanying Moon, is Mars. This 
planet revolves in an orbit, one hundred and forty-five 
millions of miles from the Sun. When Mars is at its 
greatest distance from the Earth, it is separated from 
us by a space of two hundred and forty millions of 
miles. When it is nearest the Earth, it is but fifty 
millions of miles from us. But even when nearest the 
Earth, it would require, to pass from the Earth to 
Mars, travelling at the rate of twenty miles an hour, 
about two hundred and eighty-five years. When at 
its greatest distance it would require more than a thou- 

What is drawn away from the mass of waters ? What causes the 
rising of the waters in both tides ? What planet is next beyond the 
Earth in the Solar system ? What is the distance of Mars from the Sun ? 
What is Mars' greatest distance from the Earth ? What is its nearest 
distance from the Earth ? How long would it take to reach Mars when 
nearest to us, travelling at the rate of twenty miles an hour ? How long 
would it take when Mars is farthest from us ? 



48 



THE YOUNG ASTRONOMER. 



sand years. When the Sun and Mars are on the same 
side of the Earth, Mars is said to be in conjunction. 
When the Earth is between Mars and the Sun, Mars is in 
opposition. When Mars is in opposition, Mars and the 
Earth are nearest together. Mars then appears twenty- 
five times larger than when in conjunction. The fol- 
lowing diagram will make this perfectly intelligible. 




Mars performs its annual revolution around the Sun 
in six hundred and eighty days. Thus a year on the 
planet Mars is equal to about two years on the Earth. 



When is Mars said to be in conjunction ? When in opposition ? 
When are Mars and the Earth nearest together ? How much larger 
does Mara appear when in opposition than when in conjunction ? In 
what time does Mars perform its revolution around the Sun ? How 
long is a year on Mars ? 



MARS. 



49 



It revolves in its annual orbit with a rapidity more 
than a hundred times greater than a cannon ball at its 
greatest velocity. Sir John Herschel says, that land 
and water evidently exist on the planet Mars, and that 




about one-third of its surface is water. It is also evi- 
dent that Mars is surrounded with a very dense atmo- 
sphere, in which clouds are occasionally seen floating. 
A variety of seasons must also exist upon this planet, 
somewhat similar to ours. In the winter, the northern 
regions of Mars are whitened with snow, which disap- 
pears with the return of the summer's sun. This 
planet is about four thousand miles in diameter, which 
is but one-half the diameter of the Earth. Still it is 
sufficiently large to sustain twelve times the present 



With what velocity does this planet revolve in its orbit ? What 
does Sir John Herschel say respecting Mars ? What is said of the at- 
mosphere of Mars ? What is said of the seasons on Mars ? What ap- 
pearance of snow is perceived on this planet ? What is the diameter 
of Mars ? How does that compare with the diameter of the Earth ? 
What population would Mars sustain ? 

3 



50 THE YOUNG ASTRONOMER. 

population of the Earth. No moon has yet been dis- 
covered revolving about Mars. But it is by no means 
improbable that Mars has a moon, which is undistin- 
guishable by any of our telescopes. Mars revolves 
upon its axis in about twenty-four hours, so that a day 
upon Mars is about equal to a day with us. The rota- 
tion of Mars upon its axis was discovered by the move- 
ment of spots upon its surface. Mars may be readily 
distinguished from the other planets, even by the 
naked eye, by its dark red color. Some Astronomers 
have supposed that this was owing to the nature of its 
soil. It is, however, now generally supposed to be 
caused by the exceedingly dense atmosphere which 
surrounds the planet. That Mars has a dense atmo- 
sphere, is proved from the fact that when Mars ap- 
proaches any star, the latter changes color, grows dim, 
and often disappears, even when at quite a distance 
from the body of the planet. If Mars has no moon, it 
is supposed that a compensation for the absence of a 
satellite, may be furnished by the peculiar depth and 
density of its atmosphere. The four planets, Mercury, 
Venus, the Earth and Mars, are frequently called ter- 
restrial planets. They are so called because they so 
much resemble each other. 



Has Mars a moon ? In what time does Mars revolve upon its axis ? 
How long is a day upon Mars ? How was the rotation of Mars discov- 
ered ? How may Mars be distinguished from the other planets ? To 
what have some Astronomers supposed this color to be owing ? By 
what is it now supposed to be caused ? How is it proved that Mars 
has a dense atmosphere ? What compensation may Mars have for a 
moon ? What four planets are called terrestrial planets ? Why are 
thev so called r 



MARS. 51 

1. They have a general resemblance in point of 
magnitude. 

2. They are similar in their geographical character. 

3. They have nearly the same length of days and 
nights. 

4. They are diversified with climates and supplied 
with atmospheres and clouds. 



What is their first point of resemblance ? What their second ? 
What their third ? What their fourth ? 



52 THE YOUNG ASTRONOMER. 



CHAPTER IV. 



VESTA— ASTREA— JUNO— CERES— PALLAS- 
JUPITER. 

About half way between Mars and Jupiter, five 
very small planets have been discovered. They are 
generally called the Asteroids — and have been named 
Vesta, Astrea, Juno, Ceres, Pallas. The observation of 
the immense distance between Mars and Jupiter, led 
Astronomers to imagine that there must be some inter- 
vening planet. For while the distance between the 
orbits of the Earth and Mars is but about twenty-five 
millions of miles, the distance between the orbits of 
Mars and Jupiter is over three hundred millions. In 
searching for an intermediate planet, instead of finding 
one large one, these four small ones were found. And 
various considerations have led to the supposition that 
these four planets are the fragments of some majestic 
world, which, by some terrible convulsion, has been 
blown in sunder. This supposition is rendered plausi- 
ble, 1st, by the fact that the Asteroids are not round, 

What planets are found between Mars and Jupiter ? What are they 
generally called ? What led to the discovery of these planets ? What 
is the distance between the orbits of the Earth and Mars ? What is 
the distance between the orbits of Mars and Jupiter ? What are the 
Asteroids supposed to be ? What is the first fact which supports this 
supposition ? 



VESTA ASTREA. 53 

like the other planets, but angular like irregular frag- 
ments. 

2dly. The intersection of their orbits is precisely 
the same that it would be, if they had been driven 
apart by an explosion. 

VESTA. 

Vesta is the first of the Asteroids. It is but two hun- 
dred and seventy miles in diameter, and presents a sur- 
face about equal to Great Britain, France and Ireland. 
This comparatively little globe might sustain a popu- 
lation of about sixty millions. Vesta is seldom, if ever, 
visible to the naked eye. Its revolution around the 
Sun is performed in about three years and a half. 
Though, in all probability, it revolves upon its own 
axis, the planet is so small that its diurnal revolution 
cannot be detected. Vesta was not discovered until 
the year 1807. 

ASTREA. 

A new planet has recently been discovered between 
the orbits of Vesta and Juno, which has received the 
name of Astrea. It was first recognized as a planet 
on the 8th of December, 1845, by Professor Hencke 
of Dresden, situated then between the stars of the 
ninth magnitude in the constellation of Taurus. On 

What is the second fact which supports it ? What is the first of 
the Asteroids ? What is the diameter of Vesta ? How large is its 
surface ? What population would Vesta sustain ? In what time does 
Vesta revolve around the Sun ? Does Vesta revolve upon its own axis ? 
When was Vesta discovered ? Where has a new planet recently been 
discovered ? What name has it received ? When was it discovered ? 
By whom ? In what constellation was it then seen ? 



54 THE YOUNG ASTRONOMER, 

the 14th of the same month it was seen by Professor 
Encke, and by him named by the request of the first 
discoverer. The European observers make its distance 
from the Sun two hundred and fifty millions of miles. 
It probably belongs to the group to which Sir William 
Herschel gave the name of Asteroids. And yet it is 
exceedingly difficult to imagine how it could have 
escaped the scrutiny of the twenty-six observers who, 
in the year 1800, united for the purpose of examining 
all the telescopic stars of the Zodiac, to detect that 
planet which they supposed must occupy the gap be- 
tween Mars and Jupiter. This circumstance might * 
lead to the conclusion that it is a new planet, or a 
changeable one. 

JUNO. 

The third of the Asteroids is Juno. This is con- 
siderably larger than Vesta, being estimated by some 
Astronomers to be about fourteen hundred miles in 
diameter, or nearly the size of our Moon. It is capable 
of sustaining twice the present population of the globe. 
This planet revolves around the Sun in about four 
years, and has a very dense atmosphere. 



Who next saw it ? When did he see it ? Who named it ? What 
is its distance from the Sun ? To what group does it probably belong ? 
Who named that group ? What difficulty is suggested ? To what 
opinion may this circumstance lead ? What is the third of the As- 
teroids ? How large is Juno ? What population would Juno sustain ? 
In what time does Juno revolve around the Sun ? Has Juno an atmo- 
sphere ? 



CERES PALLAS. 55 



CERES. 



The fourth Asteroid is Ceres. It is of about the same 
size with Juno, being sixteen hundred miles in diam- 
eter. In extent of surface, it is equal to about one- 
sixth of the habitable globe. If inhabited as densely 
as England, it would sustain three times the present 
population of the earth. Ceres is never seen by the 
naked eye. Its atmosphere is about seven hundred 
miles in thickness. Ceres revolves around the Sun in 
four years. The period of its diurnal revolution is 
not known. 

PALLAS. 

The fifth of the Asteroids is Pallas. Its diameter 
has not yet been ascertained. It is however supposed 
to be of about the size of the Earth's moon. Pallas 
revolves around the Sun in four years. The time in 
which it performs its diurnal revolution is not ascer- 
tained. Indeed, the Asteroids are so small that the 
size of none of them is with certainty determined. 

The assumption that the Asteroids are the fragments 
of an exploded planet helps to explain the mysterious 



What is the fourth Asteroid ? What is its size ? What is its extent 
of surface ? What population can Ceres sustain ? Can Ceres be seen 
by the naked eye? What is the thickness of its atmosphere? In 
what time does Ceres revolve around the Sun? What is the period 
of its diurnal revolution ? What is the fifth of the Asteroids ? What 
is the diameter of Pallas ? What is its supposed size ? In what time 
does Pallas revolve around the Sun ? What is the period of its diur- 
nal revolution ? What is explained by the assumption that the As- 
teroids are fragments of an exploded planet ? 



56 THE YOUNG ASTRONOMER. 

phenomenon of meteoric stones. There are hundreds 
of well-authenticated instances of showers of stones, 
some of them of very large size, falling from the sky. 
These stones do not resemble any substances which 
exist upon the Earth, while they all, in whatever part 
of the world they may fall, are similar in character. 
Five theories have been adopted by philosophers to 
explain the phenomenon of failing stones. 

1. The Atmospheric Hypothesis. This supposes 
that these stones are formed in the air, in a manner 
somewhat analogous to hail-stones. But while we can 
easily imagine that vapor may be congealed into ice, 
we cannot imagine how pure air can be consolidated 
into iron and stone. 

2. The Volcanic Hypothesis. This supposes that 
these meteoric stones are thrown from some vast un- 
known volcano on the surface of the Earth. But now 
the Earth's surface has been sufficiently explored to 
prove that there is no volcano capable of throwing 
stones to the distances where these meteoric stones fall. 

3. The Lunar Hypothesis. According to the lunar 
hypothesis, these stones are thrown from volcanic 
mountains in the Moon, called lunar volcanoes. It is 
however hardly supposable that there have ever been 
volcanoes in the Moon of such power as to throw large 
masses of stone for several thousands of miles, until 
they had passed the region of the Moon's attraction ; 
and there is no evidence that there are any volcanoes 



How many theories have been proposed to explain the phenomenon 
of meteoric stones ? What is the first hypothesis called ? What is 
this hypothesis ? What is the second ? Explain the volcanic hypo- 
thesis. What is the third hypothesis ? Explain it. 



METEORIC STONES. 57 

in the Moon, now in active operation. This theory is 
now generally abandoned. 

4. The Nebular Hypothesis. According to the neb- 
ular hypothesis, meteoric stones proceed from chaotic 
matter, which is diffused in various positions through- 
out the universe, and which is supposed to constitute 
the peculiar appearance in the heavens called nebular. 
There are, however, no reasons to be advanced in favor 
of this supposition. 

5. The Planetary Hypothesis. The supposition 
now generally advocated is, that these stones are the 
smaller fragments of that planet whose explosion, it is 
imagined, formed the Asteroids. These fragments, 
circling through the depths of space, are occasionally 
brought within the influence of the Earth's attraction. 
They then fall to the surface. Extravagant as this 
supposition may seem to be, it is the most plausible 
of any, and is the one now generally adopted. And 
still it is not easy to account for the luminous appear- 
ance which usually accompanies these falling stones, 
and their evident exposure to intense heat. 

There are very many well-authenticated instances of 
the fall of these meteoric stones. The following brief 
accounts will give a general idea of this phenomenon. 

On the 26th of April, 1803, at L'Aigle in Normandy, 
at noon of a bright and serene day, a noise was heard 
resembling thunder. A fiery ball was seen rushing 
through the atmosphere with great rapidity. It ex- 
ploded with a report which was heard for nearly a 



What is the fourth hypothesis ? Explain it. What is the fifth hy- 
pothesis ? Explain the planetary hypothesis. 

3* 



58 THE YOUNG ASTRONOMER. 

hundred miles in every direction, and immediately a 
shower of stones, with a hissing noise, was precipitated 
with immense velocity to the earth. The largest of 
the stones weighed seventeen pounds. One fell at the 
feet of a young lady standing in a yard, and rebounded 
more than a foot from the pavement. A stone grazed 
the arm of a workman, and as he attempted to pick 
it up, it was so hot that he was compelled instantly to 
drop it. The government of France deputed a distin- 
guished philosopher to repair to the spot and collect 
all the authentic facts in relation to this phenomenon. 

Several stones have fallen weighing between two 
and three hundred pounds. On the 24th of July, 
1790, one fell in the vicinity of Bordeaux and crushed 
the hut of a herdsman, killing its occupant. 

These stones are all of the same general character, 
and yet are quite different from any substances which 
are found existing upon the Earth. 

JUPITER. 

The planet which revolves next beyond the Asteroids 
is Jupiter. This is the largest orb, with the exception 
of the Sun, in the planetary system. In performing 
its vast circuit around the Sun, it occupies nearly twelve 
years, moving at the rate of twenty-eight thousand miles 
an hour ; so that a year upon that planet is equal to 



Describe the fall of meteoric stones in Normandy. How heavy have 
any meteoric stones been ? What planet comes next to the Asteroids ? 
What is the largest planet in the Solar System ? In what time does 
Jupiter revolve around the Sun ? With what speed does it revolve ? 
How long is a year upon that planet? 



JUPITER. 59 

twelve of ours. Its revolution upon its axis is accom- 
plished in about ten hours. A day and night upon 
that planet are therefore equal to but ten hours ; and 
it has more than ten thousand days in its year. This 
planet is about five hundred millions of miles from the 
Sun, and is never nearer to the Earth than four hun- 
dred millions of miles. To pass from this Earth to 
Jupiter, when w r e are nearest that planet, moving at 
the rate of twenty miles an hour, would occupy two 
thousand three hundred years. This majestic orb is 
eighty-nine thousand miles in diameter. It is equal 
in bulk to fifteen hundred such worlds as we inhabit, 
and would support a population of more than fifty 
times as many as have existed upon the Earth during 
the whole period since the creation. On the planet 
Jupiter there is very little difference in the length of 
the days and nights. We have our long summer 
days and short winter days ; but w T ith the inhabitants 
of Jupiter there is no such variety. Neither are there 
any changes from summer's burning heat to winter's 
piercing cold. The temperature in any one place is 
always essentially the same. This results from the 
fact, that the axis upon which the planet revolves is 
almost perpendicular to the plane of its orbit. Some 



How long is a day and night upon Jupiter ? How many days has it 
in a year ? What is the distance of this planet from the Sun ? What 
is its nearest distance ? How long would it take to pass from the 
Earth to Jupiter, moving at the rate of twenty miles an hour ? What 
is the diameter of Jupiter ? How much larger is it than the Earth ? 
What population would it support ? What is said of the difference in 
the length of the days and nights on this planet ? What is said of the 
changes from summer to winter ? Why is the temperature always 
essentially the same in one place ? 



60 THE YOUNG ASTRONOMER. 

astronomers have supposed that everlasting winter 
prevails about the poles of this planet; but it is alto- 
gether probable that some arrangements are adopted 
to reflect light and heat to different portions of its sur- 
face, that all its inhabitants may enjoy the benefits of 
a congenial clime. The fact that the planet, though 
at so immense a distance from the Sun, shines with 
such peculiar brilliancy, is evidence that the atmosphere 
of this majestic world is arranged to reflect the light of 
the Sun in a peculiar manner. Whether Jupiter has 
an atmosphere resembling in its properties that which 
surrounds this Earth, has not yet been ascertained. 
Lardner thinks that there is evidence of atmospheric 
currents in Jupiter, similar to those w^hich prevail on 
the Earth, blowing constantly from east to west in 
some latitudes, and from west to east in others. 

The surface of Jupiter, when seen through a good 
telescope, always presents a peculiar aspect of floating 
clouds in the atmosphere, or belts on the disc of the 
planet. It is now generally supposed that these dark 
belts are the body of the planet seen through openings 
in the brightly-illuminated clouds, which always float 
above its surface. These stripes or belts are always 
visible, with a good telescope. They are continually 
changing their form and position. Some of these belts 
are from five to ten thousand miles in breadth, and 



What have some astronomers said respecting the temperature at the 
poles of this planet ? What arrangements are probably made ? What 
fact is evidence of a peculiar arrangement to reflect light and heat ? 
Has Jupiter an atmosphere ? What is Lardner's opinion ? What 
aspect does the surface of Jupiter present ? What are those dark belts 
supposed to be ? Are these belts changeable or unchangeable ? How 
long are any of them ? 



JUPITER. 



61 



more than one hundred and thirty miles in length. 
These zones or helts are almost invariably parallel 
with the equator of the planet, and though sometimes 
for several months they exhibit no variation, yet at 
other times a belt has disappeared and a new belt been 
formed in less than two hours. The diagrams exhibit 
the general appearance of these clouds or belts, as seen 
through the telescope. 




In what direction do these belts run ? How long do they ever re- 
main permanent ? How rapidly do they ever change ? 



62 THE YOUNG ASTRONOMER. 

Jupiter has four moons. They have received the 
names, in the order of their distance from the planet, 
of Hebe, Ganymede, Themis and Metis. These names 
are, however, but little used. The satellites are gene- 
rally distinguished by the order of their distance, the 
one nearest Jupiter being called the first. Hebe re- 
volves around Jupiter in forty-two hours, that is, in 
about four of Jupiter's days. Ganymede revolves 
around the planet in eighty -five hours, or in eight and 
a half of Jupiter's days. Themis completes its revolu- 
tion in one hundred and seventy hours, or in about 
seventeen of Jupiter's days. Metis revolves around 
its primary in four hundred hours, or in forty of Jupi- 
ter's days. The first of Jupiter's satellites is a quarter 
larger than our moon ; the second is of about the 
same size with ours ; the third is seven times as large 
as our moon, and equal in size to the planet Mercury. 
The fourth is about three times the bulk of the moon. 
All these satellites, if inhabited at the rate of two 
hundred and eighty inhabitants to a square mile, would 
support a population thirty-three times greater than 
that of this Earth. These satellites can never be seen 
by the naked eye. It is a singular fact that they all, 
like our moon, revolve around their primary in the 
same time in which they revolve upon their axes. 



How many moons has Jupiter ? What names have they received ? 
How are the moons usually distinguished ? In what time does the 
first revolve around Jupiter ? In what time the second ? In what 
time the third ? In what time the fourth ? How large is the first 
satellite ? How large the second ? How large the third ? How large 
the fourth ? What population would all these satellites support ? 
Can these satellites be seen by the naked eye ? What singular fact is 
ascertained respecting the satellites of Jupiter ? 



JUPITER. 63 

The first satellite is two hundred and sixty-two thou- 
sand miles from Jupiter ; the second, four hundred 
and twenty-three thousand ; the third, six hundred 
and seventy-six thousand ; and the fourth, one million 
one hundred and eighty-nine thousand. 

It was by means of the eclipses of the satellites of 
Jupiter, that the progressive motion of light was discov- 
ered. If the motion of light were instantaneous, we 
should see an eclipse of one of Jupiter's satellites, as 
soon, when the planet is at its farthest distance from 
the Earth, as when it is nearest to us. When the 
Earth is at its greatest distance from Jupiter, it is about 
two hundred millions of miles farther from the planet, 
than when the two planets are nearest to each other. 
And it is found, that an eclipse can be seen about a 
quarter of an hour sooner, Avhen the planets are nearest 
together, than when at their greatest distance. It fol- 
lows that light, requiring a quarter of an hour to tra- 
verse a distance of two hundred millions of miles, moves 
at the rate of about two hundred thousand miles a sec- 
ond. When one of the satellites of Jupiter disappears 
from an observer on the Earth, as it goes behind the 
planet, it is said to be occulted or hidden. When it 
comes between Jupiter and the Earth, thus apparently 



What distance is the first satellite from Jupiter ? What distance 
the second ? What distance the third ? What distance the fourth ? 
What discovery has been made by means of the satellites of Jupiter ? 
What would result if the motion of light were instantaneous ? How 
much farther is Jupiter from the Earth at its greatest than at its near- 
est distance ? How much sooner can an eclipse be seen when the 
planets are nearest than when at their greatest distance ? With what 
speed does this show light to move ? When is a satellite of Jupiter 
said to be occulted or hidden ? 



64 THE YOUNG ASTRONOMER. 

passing over the surface of the planet, it is said to 
transit the disc of its primary. The nocturnal scenery 
to an inhabitant of Jupiter must be beautiful in the 
extreme. These brilliant moons are continually pass- 
ing, with great rapidity, through the heavens — some- 
times all four shining in the firmament together, exhib- 
iting a constant succession of eclipses, changes and 
occupations. An observer upon Hebe, the satellite 
nearest to Jupiter, would behold the enormous globe 
of Jupiter suspended in the heavens above him, ap- 
pearing fifteen hundred times larger than the full 
moon does to us, and filling nearly the whole firma- 
nent with its vast magnitude. It is a sublime idea, 
that this wonderful globe, peopled perhaps with count- 
less millions, is revolving upon its axis at the rate of 
twenty-eight thousand miles an hour, and circling in 
its majestic orbit, with its accompanying retinue of four 
revolving worlds, with the speed of five hundred miles 
every minute. 



When is a satellite said to transit its primary ? How large would 
Jupiter appear to an inhabitant of Hebe ? With what rapidity does 
Jupiter revolve upon its axis ? 



SATURN. 65 



CHAPTER V. 



SATURN— HERSCHEL OR URANUS 

SATURN. 

Though Jupiter is the largest planet in the Solar 
system, Saturn is, on many accounts, the most magni- 
ficent and interesting. This planet appears £ery small 
to the naked eye, and shines with a feeble light, in 
consequence of its immense distance from the Sun. 
Saturn is nine hundred millions of miles distant from 
the Sun ; a distance which it would take a cannon ball, 
at its greatest velocity, two hundred, and fifteen years 
to traverse. This planet is about eighty thousand miles 
in diameter. In bulk it is about one thousand times 
larger than the Earth. It would contain a population 
seven thousand times greater than the Earth. Though 
Saturn moves in its orbit at the rate of twenty-one 



What is considered the most interesting planet in the Solar system ? 
How does Saturn appear to the naked eye ? Why does it shine with 
such feeble light ? How far is Saturn from the Sun ? How long 
would it take a cannon ball to traverse that distance ? What is the 
diameter of Saturn ? How does its bulk compare with that of the 
Earth ? What population would Saturn sustain ? With what speed 
does Saturn revolve in its orbit ? 



66 THE YOUNG ASTRONOMER. 

thousand miles an hour, it requires thirty of our years 
for it to perform its circuit around the Sun. Its diur- 
nal revolution is performed in ten hours and a half. 
Consequently the days on Saturn, are but ten and one 
half hours in length ; while a year upon that planet 
is equal to thirty of ours. Saturn has seven satellites. 
They can, however, only be seen with the most power- 
ful telescopes, as the planet is at such an immense dis- 
tance from the Earth. The diameters of the satellites 
of Saturn have never yet been accurately measured. 
Four of the moons of Saturn revolve nearer the planet 
than is our moon to the Earth, and they appear, to an 
observer on Saturn, from twice to ten times as large. 
The largest of the moons of Saturn is at the greatest 
distance from the planet. Each of these moons prob- 
ably revolves upon its own axis, in the same time in 
which it revolves around its primary. The nearest 
satellite is but eighty thousand miles from the planet, 
and probably appears at least ten times larger than 
our moon. The second satellite, being but one hun- 
dred and twenty thousand miles distant, and undoubt- 
edly as large, at least, as our moon, must present to 



In what time does Saturn revolve around the Sun ? In what time 
is its diurnal revolution performed ? How long is a day upon Saturn ? 
How long a year ? How many moons has Saturn ? Are these moons 
visible to the naked eye ? What is said of the diameter of Saturn's 
satellites ? How many moons are nearer Saturn than our moon is to 
the Earth ? How large do these moons appear to an inhabitant of 
Saturn ? Which moon is at the greatest distance from the planet ? 
In what time do these moons probably revolve upon their axis ? What 
is the distance of the nearest satellite from Saturn ? How much larger 
does this satellite probably appear than our moon ? At what distance 
is the second satellite from Saturn ? How large is this satellite ? 



SATURN. 67 

an observer on Saturn, a disk four times larger than 
our full moon. The third satellite is one hundred and 
sixty thousand miles from its primary, and probably 
appears about four times larger than our full moon. 
The fourth and fifth moons, each, probably, about the 
same size as our own, revolve at a distance of about 
two hundred thousand miles from its primary. This 
is the distance of the Earth's moon from its primary. 
They must each present an appearance very similar 
to that of our moon. The sixth and seventh, though 
probably much larger than our moon, yet revolving 
at a much greater distance from their primary, appear 
a little smaller than ours does, at the Earth. The 
heavens must, indeed, appear gorgeously illumined 
at midnight, as an observer on Saturn looks at this 
splendid retinue of moons, suspended above him, and 
most of them passing through all their changes, in from 
two to seven days. The moons of Saturn are usually 
designated in the order of their discovery, and not in 
the order of their distance from the primary. 

The most remarkable peculiarity belonging to this 
planet is that it is surrounded by several stupendous 
rings. The number of these rings is not with certainty 
ascertained. Two of them are very conspicuous. 

How much larger will it appear than our moon ? What is the dis- 
tance of the third satellite from its primary ? How large does it ap- 
pear ? What is the probable size of the fourth and fifth satellites ? At 
what distance do they revolve from their primary ? What appearance 
do they present to the inhabitants of Saturn ? How do the sixth and 
seventh moons appear ? In what time do most of these moons pass 
through their changes ? In what order are the moons of Saturn gen- 
erally designated ? What is the most remarkable peculiarity belong- 
ing to this planet ? What is the number of these rings ? How many 
are conspicuous ? 



68 



THE YOUNG ASTRONOMER. 




These rings of vast magnitude entirely encircle the 
planet. They are evidently of a solid, compact sub- 
stance, essentially similar to the body of the planet 
itself. They are unquestionably worlds of this pecu- 
liar form, with mountains and vales, and peopled with 
millions of intelligent beings. The distance between 
the first ring and the body of the planet is about 
thirty thousand miles, so that four globes as large as 
our Earth could be placed between them. With the 
telescope, stars are easily discernible as you look 
through the space between this ring and the body of 
the planet. And this conclusively proves the separa- 
tion of the ring from the body of the planet. The 
breadth of this first or interior ring is seventeen thou- 
sand miles, which is more than twice the diameter of 
the Earth. And this ring encircles a space sufficiently 
large to contain three hundred and forty globes of the 
size of the Earth. The diameter of this ring is more 



What is the nature of these rings ? What is the distance between 
the body of the planet and the first ring ? What proves the 
separation of the ring from the body of the planet ? What is the 
breadth of the first ring ? How large a space does this ring encircle ? 
What is the diameter of this ring ? 



SATURN. 69 

than one hundred and fifty thousand miles. It would 
require seventy years for a person to travel over its 
outer circumference at the rate of twenty-five miles 
a day. This ring is about one hundred miles in thick- 
ness. About two thousand miles from this inner ring 
is an outer ring, about ten thousand miles in breadth 
and more than five hundred thousand miles in circum- 
ference. These two rings, in extent of surface, are 
nearly one hundred and fifty times larger than the 
Earth. They would sustain a population more than 
ten thousand times the present population of our 
globe. These concentric rings — themselves enormous 
worlds — are circling around their primary with the 
amazing velocity of about one thousand miles a 
minute. They revolve around Saturn in the same 
time in which Saturn revolves upon its axis. The 
wisdom of God is conspicuously displayed in the nice 
adjustments with which these vast worlds career 
onward in their endless orbits, with no interference. 
Recent observations, made at Rome, render it proba- 
ble that, instead of there being only two rings, there 
are seven independent rings, but with spaces so small 
between them, that the separation can only be distin- 
guished with the most powerful telescopes. 

These rings reflect the Solar light with peculiar 

How long would it take to traverse its circumference, at the rate 
of twenty-five miles a day ? What is the thickness of Saturn's ring ? 
What is the distance between the inner and the outer ring ? What is 
the breadth of the outer ring ? What is the circumference of the 
outer ring ? How much larger are these two rings than the Earth ? 
What population would they support ? With what velocity do these 
rings revolve ? In what time do they revolve ? How many rings is it 
now supposed that there are ? 



70 THE YOUNG ASTRONOMER. 

splendor, and consequently they must present a very 
magnificent appearance to the inhabitants of Saturn. 
In the day-time they will present the aspect of a light 
cloud, clearly defined, girdling the heavens ; but as 
the Sun goes down, this broad band will increase in 
brilliancy, encircling the sky with its effulgence, illu- 
minating the planet with almost noon-day light. As 
the inner ring is so near the planet Saturn, being but 
one-eighth part of the distance of our moon from the 
Earth, the inequalities of the surface of the ring must 
be easily discernible. Even with our telescopes, at 
such a distance, could easily be discerned many of the 
operations of their inhabitants. And these rings will 
be seen revolving with such rapidity, that any given 
point will ascend from the equator to the zenith in 
two hours and a half. It is a pleasing thought that 
if we, here on earth, are truly the disciples of the 
Redeemer, when death shall call us away, we may be 
permitted to visit these gorgeous worlds, scattered in 
infinite variety of form and beauty through the depth 
of space, there to admire their indescribable grandeur 
of scenery, and to share the joys of their happy inhab- 
itants. 

HERSCHEL. 

The planet Herschel was discovered in the year 
1781, by Sir W. Herschel. As it was discovered in 
the reign of George III. of England, the illustrious 



How will these rings appear in the day-time ? How in the night ? 
How will the distance of the inner ring compare with that of the 
Moon from the Earth ? What pleasing thought is suggested ? When 
was the planet Herschel discovered ? 



HERSCHEL. 71 

discoverer gave it the name of Georgium Sidus, or 
Georgian Star. Others named it Uranus, as Uranus 
was the father of Saturn, Saturn the father of Jupiter, 
Jupiter the father of Mars. Columbus has been 
robbed of the honor of giving the new world his 
name. The illustrious discoverer of this new planet 
ought not to be in a similar way defrauded. 

Herschel is probably the most distant planet of the 
Solar system. There may, however, be others not 
yet discovered. Its distance from the Sun is eighteen 
hundred millions of miles. In a very clear night this 
planet can be discerned by the naked eye. Its dis- 
tance from the Earth may be faintly imagined, from 
the fact that a carriage, travelling at the rate of twenty 
miles an hour, would occupy nearly ten thousand 
years in passing from this Earth to the planet. 
Herschel revolves in its orbit at the rate of fifteen 
thousand miles an hour, and yet it is eighty-one years 
in performing the vast circuit. Though the planet 
was discovered several years before the commence- 
ment of the American Revolution, it has not yet ac- 
complished one revolution around the Sun since its 
discovery. Though the length of the year upon 
Herschel has been perfectly ascertained, the length of 
its day is not yet known. Herschel is at such an im- 



What name did Herschel give the planet ? What name havejothers 
given the planet ? Why has it been called Uranus ? Is Herschel the 
most distant planet ? Can it ever be .seen with the naked eye ? What 
is the distance of Herschel from the Sun ? How long would it take a 
carriage, moving twenty mile3 an hour, to pass from the Earth to 
Herschel ? With what speed does Herschel revolve ? In what time 
does it revolve around the Sun ? What is the length of a year upon 
Herschel ? 



72 THE YOUNG ASTRONOMER. 

mense distance from the Earth that the time of its 
rotation upon its axis has not yet been ascertained. 
That it does rotate is a matter of inference, and 
not of observation. 

The diameter of Herschel is about thirty-five thou- 
sand miles. It is about eighty-one times larger than 
the Earth. It would sustain a population nearly 
fourteen hundred times greater than the present popu- 
lation of the globe. Herschel is at such an immense 
distance from the Sun, that that luminary must appear 
to its inhabitants about as large as Venus does to us. 
The Sun, however, shining not by reflected light, 
emits rays so brilliant as to give the inhabitants light 
fully equal to a cloudy day upon Earth, even if the 
constitution of the atmosphere of Herschel is similar 
to our own. There is probably, however, a peculiar 
constitution of the atmosphere, to promote the reflec- 
tion of light and heat in a manner adapted to the re- 
mote situation of the planet from the Sun. The dark- 
ness of the night is cheered by rays reflected from six 
moons, which revolve around the planet. The fact 
that Herschel is so far from the Sun is no evidence 
that it is peculiarly cold upon that planet. The de- 
gree of heat is not in proportion to the distance of a 
body from the Sun. Even upon the equator a moun- 
tain elevation of fifteen thousand feet brings one to 

What is the diameter of Herschel ? How large does the Sun ap- 
pear to the inhabitants of Herschel ? How much larger is Herschel 
than the Earth ? How light would this make a day upon Herschel ? 
What peculiar constitution of the atmosphere may probably be adopt- 
ed ? How is the darkness of the night cheered ? Is it necessarily 
very cold upon Herschel ? At what elevation on the equator is per- 
petual snow ? 



HERSCHEL. 73 

the region of perpetual snow. There may be, conse- 
quently, some arrangement by which the warmth of 
our central luminary may fall as genially upon the 
hills and valleys of Herschel as upon the verdant 
slopes of sunny Italy. It is highly unphilosophical 
to suppose that upon all the planets the constitution of 
Nature is the same. Intelligent beings, of far different 
bodily structure and wants from the inhabitants of the 
Earth, probably rejoice in the dwellings of those gor- 
geous creations of the Deity. 

The magnitude of the satellites of Herschel has 
never yet been precisely ascertained. It is probable, 
however, that these satellites are considerably larger 
than our moon, else they could hardly be seen, even 
with the telescope, at such a vast distance from the 
Earth. If these six moons are three thousand miles 
in diameter, they will sustain, unitedly, a population 
of more than sixty times as many as now dwell upon 
the Earth. It is a remarkable peculiarity in these 
satellites, that they all revolve around their primary 
from east to west, while every other primary and 
secondary satellite in the Solar system revolves around 
its central body in an opposite direction — from west to 
east. 

If all the planets of the Solar system were inhabited 
as densely as the island of Great Britain, they would 
sustain a population more than twenty-seven thou- 

What is said respecting the constitution of nature upon the several 
planets ? What is said of the magnitude of HerscheFs satellites ? 
What is their probable magnitude ? What population will the moons 
of Herschel probably sustain ? "What remarkable peculiarity is there 
in the revolution of these satellites ? How laige a population will all 
the planets of the Solar system sustain ? 
4 



74 THE YOUNG ASTRONOMER. 

sand times greater than now peoples the Earth. 
And yet, the Sun is five hundred and forty-five 
times larger than all these planets taken together. 
And it is supposed that this immense globe, with all 
its retinue of revolving worlds, is flying through space 
at the rate of sixty thousand miles an hour, circling* 
around some distant and unknown centre which no 
telescope has ever yet revealed to human eyes. It 
has been well said, that " an undevout astronomer is 
mad." Who can contemplate these sublime ideas 
and not look forward with interest to the hour when 
the liberated soul may soar amid these wonderful 
orbs ? And, in view of this blessedness — doubtless 
reserved for the humble disciple of Jesus — who can 
refrain from breathing the prayer, a Oh ! that I may 
die the death of the righteous P 



What is the comparative size of the Sun ? How rapidly is the Sun 
supposed to be moving ? 



COMETS. 



75 



CHAPTER VI. 



COMETS. 

There is connected with the Solar system, besides 
the planets, a large number of mysterious bodies, called 
Comets, Comets are bodies having no definite shape, 
and consisting mainly, not of solid, but vaporous or 
aeriform substance, which usually appear unexpectedly 
in our system, and rushing, with great velocity, around 
the Sun, again disappear in the depths of space. The 
meaning of the word Comet, is a hairy star. They 
are so called because they are usually accompanied by 
a long train resembling luminous hair. 

Respecting the physical constitution of Comets but 
little is known. They usually consist of three parts. 
The first is a brilliant spot called the nucleus. This is 
probably a highly condensed gaseous or vaporous sub- 
stance. The nucleus may, in some cases, be solid; 
but that this is not usually the case is evident from the 
fact, that stars can be often seen through the nucleus. 
The nucleus is generally surrounded by a hazy or 
nebulous covering, called the envelope^ or coma. And 
there is usually connected with this nucleus a long 

What is connected with the Solar system besides planets ? What 
are Comets ? What is the meaning of the word Comet ? Why are 
they so called ? What is said of the physical constitution of Comets ? 
Of how many parts do they usually consist ? What is the first ? What 
is the nucleus ? What is the evidence that it sometimes is Dot solid ? 
With what is the nucleus generally surrounded ? 



76 THE YOUNG ASTRONOMER. 

fan-like appendage, called the train or tail. The en- 




velope and train are always composed of a substance 
somewhat resembling the thinnest fog. The interpo- 
sition of this exceedingly rare substance, though per- 
haps a hundred million of miles in thickness, does not 
obstruct the rays of light twinkling from the feeblest 

What other part is generally connected with the nucleus ? Of what 
is the envelope or train composed ? What is said of the density of the 
train of a Comet ? 



COMETS. 



77 



star. Newton, indeed, has expressed the opinion, that 
this luminous haze is so inconceivably rare, that 
if the tail of the largest Comet which was ever seen, 
were compressed to the consistency of atmospheric air, 
it would not occupy, in bulk, the space of one cubic 
inch. Whether, in any case, the nucleus of a Comet 
is solid, is a question not yet decided. Comets vary 
so much in appearance, that while some have no nu- 
cleus, others have no train or tail. Those Comets 
without a train are usually called bearded comets. One 
may be seen illustrated in the accompanying diagram. 




What opinion has Newton expressed ? Is the nucleus ever solid ? 
What is said of the variety in the appearance of Cornets : What are 
bearded Comets ? 



78 THE YOUNG ASTRONOMER, 

Comets do not permanently remain the same, but are 
often changing their appearance, sometimes as rapidly 
and fantastically as the northern lights. 

Comets vary exceedingly in size. While some pre- 
sent themselves, merely as a tuft of down upon the 
sky, others sweep, with their enormous trains, millions 
of miles through the immensities of space, extending 
with their pale and portentous glare from the zenith to 
the horizon. Some Comets are seen with a nucleus 
but twenty-five miles in diameter, while others have 
a nucleus many thousand miles in diameter. The tail 
of a Comet which appeared in the year 1811, was es- 
timated to be one hundred and thirty-two millions of 
miles in length, its nucleus was fifty thousand miles in 
diameter, and the nucleus, with the envelope, nine 
hundred and forty-seven thousand miles in diameter, 
which is larger than our Sun. Most Comets are only 
visible through the telescope. 

The number of Comets which have visited the Solar 
system, is estimated to be as many as seven millions ; 
others have calculated the number to exceed five hun- 
dred millions. But a few hundred, however, of these 
have been seen by the inhabitants of the Earth. Seven 
or eight hundred only have been observed since the 
commencement of the Christian Era. They suddenly 
burst upon our view, rushing into our system from 



What is said of the changes in the appearance of Comets ? What 
is said of the size of Comets ? How small is the nucleus of any 
Comet ? How large is any ? How long was the train of the Comet of 
1811 ? What was the size of its nucleus ? What the size of the nu- 
cleus with the envelope ? What is said of the number of Comets 
which have visited our system ? In what direction do they come ? 



COMETS. 



79 



every conceivable direction, revolving in various kinds 
of orbits, with different degrees of velocity, some ap- 
proaching very near the Earth, and others not coming 
within millions of miles of our orbit. 

The time required in the periodic revolution of 
Comets is very various. The three Comets whose or- 
bits have been measured, and whose periodic return 
have been satisfactorily established, are Encke's, Hal- 
ley's, and Biela's. They are so named from distin- 
guished philosophers who calculated their periods. 
Encke's Comet performs its revolution in three years 
and a half. Its orbit does not extend beyond the verge 
of the Solar system. This Comet is very small, has 
no tail, and is invisible to the naked eye. Halley's 
Comet performs its revolution in seventy-five years. 
It is very large, and distinctly visible to the naked eye. 
It rushes in an exceedingly elongated orbit, to the dis- 
tance of two thousand millions of miles beyond the or- 
bit of Herschel. This Comet made its last appear- 
ance in 1835, and is now rushing along its almost 
limitless pathway, not again to appear in our even- 
ing sky until the year 1910. Biela's Comet completes 
its revolution in a little less than seven years. Other 
Comets are supposed to revolve in orbits, which it re- 



What is their speed ? How near do they approach the Earth ? 
What three Comets have had their periodic returns calculated ? In 
what time does Encke's Comet revolve in its orbit ? How far does its 
orbit extend ? What is the size of this Comet ? Is it visible to the 
naked eye ? In what time does Halley's Comet perform its revolution ? 
What is the size of this Comet ? Is it visible to the naked eye ? How 
far does its orbit extend ? When did this Comet make its last ap- 
pearance ? When will it again appear ? In what time does Biela's 
Comet perform its revolution ? What is said of other Comets ? 



80 THE YOUNG ASTRONOMER. 

quires several thousands of years to traverse ; while 
others visit our system, and depart never to return. 
The following diagram will show the elongated form 
of the orbit of a Comet. 




The purposes which Comets are intended to subserve 
are entirely unknown. Various suppositions have 
been suggested by Astronomers, but none of them have 
obtained any general approval. Sir Isaac Newton has 
expressed the opinion, that Comets were intended to 
replenish Suns with the light and heat they lost by 
radiation. Others have supposed that they were em- 
bryo worlds, which, in process of time, by union and 



What purposes do Comets subserve ? What opinion has Sir Isaac 
Newton expressed ? What opinion have others expressed ? 



COMETS. 81 

consolidation, would form new suns and planets. These 
are, however, merely conjectures. 

Whether Comets shine by their own light, like suns, 
or by reflected light, like the planets, has been long 
undecided. 



Do Comets shine by their own or reflected light ? 
4* 



82 THE YOUNG ASTRONOMER. 



CHAPTER VII. 



THE FIXED STARS. 

Having thus briefly examined the several bodies 
which compose the Solar system, we will now turn 
our attention to the Fixed Stars , which we see twink- 
ling in the depths of space above and around us. 

THE NUMBER OF FIXED STARS. 

The number of Fixed Stars visible to the naked eye 
in a clear night is about one thousand. By the aid 
of the telescope innumerable other stars are brought 
into view, so that more than one hundred millions of 
these gorgeous suns, each unquestionably surrounded 
by its retinue of worlds, are distinctly seen. If we 
suppose that each of these suns is accompanied only 
by as many planets as are embraced in our Solar sys- 
tem, we have three thousand millions of worlds in our 
own firmament. No human mind can form a concep- 



To what is the attention now to be directed ? How many fixed 
stars are visible to the naked eye ? How many are visible through 
ordinary telescopes ? How many worlds are there probably in our 
firmament ? 



CONSTELLATIONS. 83 

tion of this number ; but even these, as will hereafter 
be shown, form but a minute and comparatively insig- 
nificant portion of that boundless empire which the 
Creator has reared, and over which he reigns. Eternal 
ages may glide joyfully along, as the Christian explores 
these wonderful worlds, of every variety of form and 
character, and partakes of the hospitalities of their 
blissful inhabitants. It is pleasant to tread the pave- 
ments of a foreign city — to traverse the glaciers of the 
Alps — to glide over the surface of the Nile in the midst 
of the mouldering memorials of its past grandeur; 
but what are all these, compared to the journey of a 
rejoicing spirit to these sublime mansions of the Deity? 

CONSTELLATIONS. 

That the stars may be more easily distinguished 
from each other, and their places in the heavens de- 
fined, the ancients have divided them into groups or 
clusters, called constellations. These constellations 
have been very fancifully named after some animal 
or object, which it is supposed might be easily delin- 
eated in the space which the group occupies. When, 
however, we look upon the celestial globe or upon the 
starry heavens, we can scarcely discern any resem- 



What is said respecting the conception of such numbers ? What is 
said respecting the comparative importance of these worlds ? What 
pleasant thought does this introduce to the Christian ? By whom 
were the stars arranged into clusters called constellations ? Why 
was this done ? How were the constellations named ? Can any re- 
semblance be traced between the figures of the constellations and the 
objects whose names they bear ? 



84 THE YOUNG ASTRONOMER. 

blance between the actual figure of the groups of stars 
and the objects whose names they bear ; and the en- 
deavor to trace out any resemblance only embarrasses 
the mind. The number of constellations into which 
the visible stars have been arranged is ninety-three. 
Of these, thirty-four are in the northern firmament, 
and forty-seven in the southern firmament, and also 
twelve in that portion of the heavens called the Zodiac. 
The zone called the Zodiac is sixteen degrees broad. 
The apparent path of the Sun, and the orbits of all the 
planets except three of the Asteroids, are within this 
zone. This zone is divided into twelve equal parts, 
called the twelve signs of the Zodiac. The signs of 
the Zodiac and the constellations of the Zodiac, pos- 
sessing a common name, had doubtless formerly a 
common origin. About two thousand years ago the 
signs and the constellations were probably together. 
They now, how 7 ever, vary about thirty degrees. The 
Sun enters the sign of 

1. Aries Y, the Ram, the 20th of March ; 

2. Taurus «, the Bull, the 20th of April ; 

3. Gemini n, the Twins, the 21st of May; 

4. Cancer £2, the Crab, the 21st of June ; 

5. Leo £X, the Lion, the 23d of July ; 

6. Virgo % the Virgin, the 23d of August ; 

7. Libra =£=, the Balance, the 23d of September ; 



How many constellations are there ? How many of these are in 
the northern firmament ? How many in the southern firmament ? 
What is the breadth of the Zodiac ? What heavenly bodies move 
within this zone ? Into what is this zone divided ? When were the 
signs and constellations probably together ? How much do they now 
vary ? At what time does the Sun enter the several signs ? 



CONSTELLATIONS. 85 

8. Scorpio rn, the Scorpion, the 23d of October; 

9. Sagittarius t , the Archer, the 23d of November ; 

10. Capricornus VS, the Goat, the 23d of December ; 

11. Aquarius 2£, the Waterman, the 20th of January; 

12. Pisces X, the Fishes, the 19th of February. 

As the first six of these signs lie on the north side of 
the equator, they are called the northern signs. The 
remaining six, being on the south side of the equator, 
are called the southern signs. The signs Capricornus, 
Aquarius, Pisces, Aries, Taurus, Gemini, are called 
ascending signs, because the Sun is then apparently 
advancing from the equator towards the north pole ; 
and Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, 
are called descending signs, as the Sun is retiring from 
the north pole as it passes through them. The path 
which the Sun appears to traverse through the heavens 
is called the ecliptic. The point where the Sun crosses 
the equator moves back about fifty seconds of a degree 
each year, and in about twenty-six thousand years 
this point will have moved entirely round the equator. 
This backward movement of the point where the 
ecliptic and the equator intersect each other, is called 
the Precession of the Equinoxes. 

This division of the stars into constellations is of 
very ancient date. Job refers to some of these con- 
stellations by the names which they now bear. 



What are the northern signs ? What are the southern ? What are 
the ascending signs ? What are the descending signs ? What is the 
ecliptic ? How far does the point where the ecliptic and the equator 
intersect each other move each year ? What is the Precession of the 
Equinoxes ? 



86 THE YOUNG ASTRONOMER. 



MAGNITUDE OF THE STARS. 

It is impossible to determine with precision the real 
magnitude of the fixed stars. Their distance is so 
immense, that though we take the whole diameter of 
the earth's orbit as a base-line, from either end of this 
line the star still seems in the same position. The 
diameter of the earth's orbit is about two hundred 
millions of miles ; and this vast line is an almost micro- 
scopic point, when compared with the interminable 
expanse Avhich intervenes between the eye and yonder 
twinkling star. No power of the telescope will cause 
the stars to assume any apparent diameter. They 
appear through the most powerful instruments as mere 
points of the most piercing brilliancy. From various 
calculations, it is evident that none of the stars are 
smaller than our sun ; and it is probable that many 
of them are far superior to the Sun in magnitude and 
splendor. 

Dr. Wollaston has inferred, from arguments founded 
upon the intensity of light, the star Sirius to be at least 
fourteen times larger than our sun ; and Sir William 
Herschel has estimated the star Vega to surpass in 
magnitude fifty-four thousand globes as large as the 



What is said of the real magnitude of the fixed stars ? What fact 
illustrates their immense distance ? What is the diameter of the 
Earth's orbit ? Have the fixed stars any apparent diameter ? How- 
do they appear through the most powerful telescopes ? How small 
are any of them ? What is the apparent magnitude of some ? What 
is said of the star Sirius ? Upon what is this opinion founded ? What 
is HerschePs opinion of the size of the star Vega ? 



MAGNITUDE OF THE STARS. 87 

Sun. The Sun is more than five hundred times greater 
than all the planets and satellites of our system united. 
Of such magnitude it is impossible for the human mind 
to form any conception. How utterly inconceivable 
is a globe fifty-four thousand times greater than the 
Sun. When we look upon these twinkling lights, 
and imagine the variety of structure and scenery with 
which they abound, and think of the myriads of lofty 
intelligences with which they are undoubtedly peo- 
pled, how greatly does it enlarge our ideas of the 
grandeur of the Creator's works. During all the 
revolutions of an interminable existence, the Christian 
will ever find an inexhaustible supply of objects for 
sublime and delighted contemplation. 

The stars are also divided by astronomers into dif- 
ferent classes, called magnitudes. They are guided 
in this classification by the comparative brilliance with 
which the stars shine. The most brilliant are called 
stars of the first magnitude; those a little less brilliant 
of the second, and so on to the sixth magnitude. The 
smallest stars visible to the naked eye are called those 
of the sixth magnitude. With the use of the telescope 
the classification is still carried on to stars of the twen- 
tieth magnitude. 



What is said of the magnitude of the Sun ? What moral reflection 
does this subject suggest ? How are the stars classified by Astrono- 
mers ? What are the most brilliant stars called ? What are the small- 
est visible to the naked eye called ? How far is the classification 
carried ? 



88 THE YOUNG ASTRONOMER. 

VARIETY IN THE STRUCTURE OF THE STARS. 

On this globe we find great variety in the works of 
the Creator. As we raise our eyes to the Solar system, 
we perceive there a similar display of the profusion of 
creative power. Jupiter rolls along his majestic path- 
way, encircled by belts and accompanied by his beau- 
tiful household ; and Saturn, w r ith his gorgeous rings, 
rushes through his almost boundless orbit; and comets 
— ethereal and spiritualized worlds — come careering 
onward through the depths of space, adapted for the 
residence of beings of whose structure and nature we 
can form no idea ; and the Sun, with its unchanging 
heat and its eternal day, adds still new variety to this 
scene of grandeur. As we leave the Solar system and 
wing our flight to that vast profound where the fixed 
stars repose, we behold indications of still continued 
variety, not only in the magnitude of those orbs, but 
also in their internal structure. When these stars are 
examined through powerful telescopes, they assume a 
great variety of colors. One appears of a brilliant 
orange color, another green, another blue, another 
red. There is undoubtedly a vast diversity in respect 
to magnitude. As one single drop of water affords a 
home for myriads of living creatures, where they may 
revel in an expanse to them apparently limitless, so 



What is said of the works of the Creator on this globe ? What is 
said respecting variety in the Solar system ? What is Jupiter's ap- 
pearance ? What is the appearance of Saturn ? What is said of comets ? 
What variety is perceived in the fixed stars ? How do they appear 
through powerful telescopes ? 



DISTANCES OF THE STARS. 89 

there may be globes even of microscopic diminutive- 
ness, peopled by busy millions, who there find, for 
them, an almost boundless domain; while other orbs 
may swell out to an interminable grandeur, compared 
with which our sun itself dwindles into an insignificant 
point. Some of the stars shine with their own light, 
while there may be others, of equal magnitude, invis- 
ible to us because illuminated only by rays from dis- 
tant luminaries. Many of these vast orbs are solid, 
material worlds ; and there are others, of a magnitude 
surpassing all powers of the imagination to conceive, 
which are gaseous or ethereal in their nature, adapted 
probably for the residence of beings of whose nature 
we can form no conception. But in the interminable 
expanse of these immaterial worlds, spreading for 
countless myriads of miles through these immensities, 
beings allied to cherubim and seraphim may raise their 
ceaseless and exulting hosannas. 

DISTANCES OF THE STARS. 

The distance of the Sun from the Earth, and of the 
various planets which compose our Solar system from 
the Sun, and from each other, has been measured with 
much accuracy ; and those distances are so enormous 
that no human mind is capable of comprehending 
them. No mind can embrace the idea of a single 
million ; but the Sun is ninety-five millions of miles 



What is said respecting variety in magnitude ? In what respect 
may the stars differ in structure ? What distances in the heavens 
have been accurately measured ? Can these distances be compre- 
hended ? 



90 THE YOUNG ASTRONOMER. 

from the Earth. Though we cannot tell how far the 
fixed stars are from the Earth, it is susceptible of de- 
monstration that none of them can be nearer than 
twenty billions of miles. Some faint conception of 
this distance may be acquired from the statement that 
a cannon ball, flying five hundred miles an hour, 
would require four millions, five hundred and ninety- 
five thousand years before it could pass that distance. 
While it is certain that none of the fixed stars are 
nearer the Earth than the distance thus stated, from 
various calculations it is estimated that the star 61 
Cygni is at such a distance from the Earth, that a 
steam carriage, moving with the velocity of four hun- 
dred and eighty miles a day, would require more than 
three hundred and fifty millions of years in passing 
from this Earth to the star. And yet there are many 
stars revealed by the telescope which must be several 
thousand times farther distant than 61 Cygni. And 
though these numbers and ideas bewilder the mind, 
these distances are but minute and indivisible points, 
compared with that vast infinity of space which the 
Creator has crowded with worlds. The numbers 
which can be embraced within the reach of the tele- 
scope are probably insignificant in comparison with 
the majestic whole. 



At what distance is the Sun from the Earth ? Can the distance of 
the fixed stars from the Earth be measured ? What fact respecting 
their distance is susceptible of demonstration ? What illustration is 
given of the distance of twenty billions of miles ? What is said of the 
distance of the star 61 Cygni ? What is said of other stars still more 
remote ? What proportion of the stars is probably embraced within 
the reach of the telescope ? 



NEW STARS AND LOST STARS. 



NEW STARS AIND LOST STARS. 



91 



There must have been a time when each star was 
created. Whether the formation of the stars was a 
gradual or a sudden process, we cannot determine ; 
but since the Christian era there have been several 
instances in which stars have suddenly appeared in 
the sky, as if they had just been launched forth fresh 
from the Creator's hand. In November, 1572, a very 
brilliant star suddenly appeared in the constellation 
Cassiopeia. This star was so brilliant as to attract 
general attention, and was even visible at noon-day. 
It continued to shine with gradually diminishing lustre 
for about sixteen months, when it disappeared. This 
star was far beyond the planets, in the region of the 
fixed stars. The cause of its sudden appearance, and 
of its gradual disappearance, is of course involved in 
profound obscurity. Some have supposed that it was 
the conflagration of some distant world, whose rays 
were thrown across the vast abysses of space to gleam 
upon human eyes. Others have supposed that it was 
some vast sun circling in its majestic orbit, and that 
it was visible in its nearest approach to the Earth, 
and that it gradually vanished again as it retired. 
This, however, would hardly account for its sudden 
appearance. 

In the year 1804 a new star appeared in the con- 
Have the stars existed from eternity ? Was each one suddenly or 
gradually created ? What is said respecting the appearance of new 
stars ? Describe the new star of 1572. To what cause have some 
attributed the appearance of this star ? To what cause have others 
attributed its appearance ? 



92 THE YOUNG ASTRONOMER. 

stellation Serpentarius. It shone with a brilliancy 
surpassing that of any of the fixed stars ; and, what 
was very remarkable, it was continually changing into 
all the colors of the rainbow. This star also gradually 
disappeared in about a year. It was in the region of 
the fixed stars, and continued apparently immovable 
in its position. Says Mrs. Sommerville, u It is impos- 
sible to imagine anything more tremendous than a 
conflagration that would be visible at such a distance." 
Says Dick, u There was a splendor concentered in 
that point of the heavens where the star appeared, 
more than equal to the blaze of twelve hundred thou- 
sand worlds such as ours, were they all collected into 
one mass and all at once wrapt in flames. Nay, it is 
not improbable that, were a globe as large as would 
fill the whole circumference of the Earth's annual 
orbit to be lighted up with a splendor similar to that 
of the Sun, it would scarcely surpass in brilliancy and 
splendor the star to which we refer." 

Says La Place, u As to those stars which suddenly 
shine forth with a very vivid light and then vanish, 
it may be supposed, and with probability, that great 
conflagrations, occasioned by extraordinary causes, 
take place on their surfaces ; and this supposition is 
confirmed by their change of color, analogous to that 
which is presented to us on the Earth by bodies which 
are consumed by fire." 



In what constellation did the star of 1804 appear ? What is said of 
its brilliancy ? What remarkable appearance did it assume ? How 
long was this star visible ? Where was its position ? Repeat Mrs. 
Sommerville's remark. Repeat Dick's remark. Repeat the remark 
of La Place, 



VARIABLE STARS. 93 

Says Dr. Mason Good, "What has befallen other 
systems will assuredly befall our own. Of the time 
and the manner we know nothing; but the fact is 
incontrovertible — it is foretold by revelation — it is in- 
scribed in the heavens — it is felt through the Earth." 
The Word of God has informed us that " the elements 
shall melt with fervent heat, and the Earth and the 
works that are therein shall be burned up. 3 ' It is, 
however, to be remembered that combustion is not 
annihilation. After the conflagration of this globe, 
the particles of which it is composed will remain as 
before, only changed in their combinations ; and from 
the ruins there may be created a new earth, wherein 
shall dwell righteousness. " Within the last century," 
says Dick, " no less than thirteen stars in different 
constellations seem to have totally perished, and ten 
new ones to have been created." 

VARIABLE STARS. 

Those stars are called variable, which have periodic 
changes in their apparent magnitude and brilliancy ; at 
one time shining with great splendor, and then gradu- 
ally fading away, till they become quite dim or entire- 
ly disappear. About thirty-seven sucji stars have been 
discovered. Some of these stars pass through these peri- 
odic changes in about a year. Others disappear, and 



Repeat the remarks of Dr. Mason Good. Repeat the quotation 
from the Bible. What will remain after the final conflagration ? How- 
many stars have apparently been destroyed within the last century ? 
How many new ones have been formed ? What are variable stars ? 
How many variable stars have been discovered ? In what time do 
some of these pass through their periodic changes ? 



94 THE YOUNG ASTRONOMER. 

are not again visible for several years. One remark- 
able star in the constellation Perseus, is continually 
passing through the changes, from a star of the first 
magnitude to one of the fourth, in about two days and 
a half. It is very difficult to come to any satisfactory 
conclusion respecting the cause of this phenomenon. 
Various theories, however, have been proposed to ac- 
count for these appearances. 

FIRST THEORY. 

Sir William Herschel suggests that one hemisphere 
of these globes may be covered with dark spots, or be 
less brilliant than the other, and that the revolution of 
the globe at one time presents the more luminous sur- 
face, and at another the less. 

Clear Hemisphere. Spotted Hemisphere. 





SECOND THEORY. 



Again, it has been suggested that these variable stars 
may not be globes, but circles, like a grindstone in 



What is the case with others ? What is said of a star in the con- 
stellation Perseus ? What is the cause of this phenomenon! ? De- 
scribe the first theory. The second. 



VARIABLE STARS. 



95 



form ; and, sts they revolve, at one time the broad sur- 
face is presented to the eye, and again only the edge. 



Side View. 



Edge View, 





THIRD THEORY. 

Again, it has been supposed that some large planet 
may be revolving around the luminary, and by the in- 
terposition of its opaque body, may cut off the rays of 
light. 

The white globe in the cut represents a glittering star over whose 
surface a dark planet revolves periodically, diminishing its lustre. 




Describe the third theorv. 



96 THE YOUNG ASTRONOMER, 

FOURTH THEORY. 

It is also suggested, as possible, that there may be 
planets of majestic size, vastly surpassing our sun in 
magnitude, around which a sun of lesser magnitude 
revolves, and that in its revolution it is periodically 
hidden behind the planet. 

The dark globe in the cut represents a majestic planet, behind which 
its revolving sun gradually and periodically disappears. 




FIFTH THEORY. 

The phenomenon may be caused by a vast sun, 
" moving with inconceivable velocity in an immensely 
elliptical orbit, the longer side of which is nearly in a 
direction to our eye." 

Let E be the Earth. The star revolves in the orbit A B C D, 
disappearing in the distance, as it passes towards the extreme of 



Describe the fourth theory. The fifth. 



VARIABLE STARS, 97 

its orbit, at C, and shining with ever increasing lustre as it ap- 
proaches A. 



E 

3 




Whatever may be the cause, the fact of these varia- 
tions is perfectly established, and the contemplation of 
the stupendous changes which must be occurring in 
those distant orbs, overwhelms the mind with amaze- 
ment. Worlds vastly larger than our sun suddenly 
appear, and as suddenly disappear — now they blaze 
forth with most resplendent brilliancy, and again they 
fade away — and often are apparently blotted from ex- 
istence. These worlds are unquestionably thronged 
with myriads of inhabitants. And the phenomenon 
which to us appears but as the waxing or waning lus- 
tre of a twinkling star, may to the dwellers on those 
orbs, be evolutions of grandeur, such as no earthly 
imagination has ever conceived. But these scenes, now 
veiled from human eyes, will doubtless all be revealed, 
when the Christian shall ascend on an angel's wing to 
the angels' home. 



What is said of the fact of these changes ? Describe the appearance 
of these variations. Are these worlds probably inhabited ? How 
may the phenomenon appear to dwellers on those orbs ? When will 
these scenes probably be revealed ? 

5 



98 THE YOUNG ASTRONOMER. 

DOUBLE STARS. 

As the planets revolve around the Sun, so it is as- 
certained that in very many cases two stars mutually 
revolve around each other. About six thousand of 
these double stars have been discovered, and carefully 
arranged in catalogues. These stars are generally so 
near each other, as to appear to the naked eye as one ; 
but by the telescope they are seen to be separated. 
The periods of their revolutions have, in several cases, 
been ascertained. 

A star revolves around the star Castor, in about three 
hundred and fifty years. In the constellation Virgo, 
there is a double star whose revolution is estimated to 
occupy about six hundred years. In the constellation 
Leo, there is a double star whose revolution occupies 
about twelve hundred years. These stars revolve in 
elliptical orbits, similar to those in which the planets 
revolve around the Sun. 

The discovery of these double stars opens to the 
mind a new chapter in Astronomy. We here see suns 
revolving around suns, each unquestionably accom- 
panied by its retinue of revolving worlds. 

Though the apparent distance between these stars 
composing binary systems is so small, it is supposed 
that they are in reality separated by a distance as great 

What is meant by double stars ? How many of these have been dis- 
covered ? How do these stars appear to the naked eye ? How do they 
appear through a telescope ? What is known respecting their revolu- 
tions ? What is said of the star Castor ? What is said of the double 
star in the constellation Virgo ? What is said of the double star in 
the constellation Leo ? In what kind of orbits do these stars revolve ? 
What is the probable distance between the stars which compose these 
systems ? 



COLORED SUNS. 99 

as that between the Earth and any of these stars. The 
size of these bodies, visible at such an immense dis- 
tance, must be enormous ; and the velocity with which 
they are impelled in their stupendous orbits, must very 
far exceed that of any of the planetary bodies. The 
mind is elevated by the attempt to contemplate ideas 
of such grandeur. 

COLORED SUNS. 

" Many of the double stars," says Sir J. Herschel, 
" exhibit the beautiful and curious phenomena of con- 
trasted or complementary colors. In such instances, 
the larger star is usually of a ruddy or orange hue, 
while the smaller one appears blue or green." 

The scenery of a world illuminated to-day by a 
green sun, and to-morrow by an orange one, must be 
singular indeed. And this variety in the mansions of 
the Creator must contribute greatly to the enjoyment 
of those who may hereafter be permitted to wing their 
flight from world to world, and from star to star. 
These stars shine in nearly all the various colors of 
the rainbow. In the clear atmosphere of tropical 
climates, this variety in the color of the stars is quite 
perceptible to the naked eye. Stars also change their 
colors. Sirius was by the ancients called a red star ; 
it is now brilliantly white. 

What is said of the size and velocity of these revolving suns ? 
What does Herschel say respecting the color of double stars ? Of 
what color is the larger star generally ? Of what color the smaller ? 
What is said of the scenery of worlds thus illuminated ? What va- 
rious colors do the stars assume ? How do these stars appear in trop- 
ical climates ? Do stars ever change their color ? What example 
of this is given ? 



100 THE YOUNG ASTRONOMER. 

TRIPLE AND MULTIPLE STARS. 

In addition to binary systems, there are also triple, 
quadruple and multiple stars. And the various stars 
of which these systems are composed harmoniously 
revolve around each other. Such systems must be ex- 
ceedingly complex. Unquestionably, each star, like 
our sun, is the centre of a system of planetary worlds, 
and each member of the system must exert an attract- 
ive influence upon all the rest. There are no earthly 
intellects capable of determining the courses described, 
and the perturbations produced, by such combinations. 
But the contemplation of them elevates our ideas of 
the wisdom and power of the great Creator, and exalts 
our conceptions of the profusion of beauty and variety 
with which immensity is filled. 

OUR FIRMAMENT. 

The stars, instead of being about equally scattered 
through space, appear to be clustered together in vast 
groups of many millions. These groups, or firma- 
ments^ as they are called, are separated from each 
other by measureless depths of apparently unoccupied 
space. The stars composing these firmaments are 
clustered together in forms of every conceivable va- 
riety. All the stars visible by the naked eye, and 



What systems are found besides binary systems ? What is each 
star probably ? Can the various movements produced by these com- 
plicated influences be easily described ? Are the stars equally diffused 
through space ? What are these groups called ? How are these 
firmaments separated from each other ? What forms do these firma- 
ments assume ? What stars belong to our firmament ? 



OUR FIRMAMENT. 101 

nearly all seen through telescopes of ordinary power, 
belong to the cluster composing our firmament. The 
number of suns thus congregated together, with their 
accompanying retinue of planetary worlds, is probably 
not less than three thousand millions. 




The general form assumed by the millions of stars 

Of how many worlds does our firmament probably consist ? What 
is the general form of our firmament ? 



102 



THE YOUNG ASTRONOMER. 



which compose our firmament is that of a circle, some- 
what resembling a grindstone. Nichol thus describes 
the general form of our firmament, as ascertained by 
the very laborious and accurate observations of Her- 
schel. " You know a common grindstone ? Suppose 
first, that the rim is split in the middle, along the line 
of the rim, and through about one-third of its circum- 
ference ; which split, however, does not reach so far 
down as the centre of the grindstone ; also, let the 
divided parts be somewhat separated towards the mid- 
dle of the division, so that they run along and re- 
enter after a temporary separation." The following 
plate exhibits, first a side view, and secondly an edge 
view, of the form of our firmament. 



Side View. 



Edge View, 





" Suppose, secondly, that the grindstone is considerably 
more porous than stone is. Then, let its minute atoms 
represent stars, the pores, or intervals, representing 
the spaces between the stars ; and observe what an 
inhabitant of a sun or world, near the centre of a clus- 
ter of such configurations, would perceive in his hea- 



Repeat NichoPs illustration of the form of our firmament. 



OUK FIRMAMENT. 103 

vens. They would be precisely similar to our own 
celestial vault. Towards their sides the view would 




be comparatively unadorned— dark space, looming 
from behind the visible stars-; while^ in the direction 



104 THE YOUNG ASTRONOMER. 

of the circumference, a countless mass of small, remote 
stars would, although separately unseen, illumine the 
sky, forming a splendid zone, divided, like our Milky 
Way, through part of its shadowy course." u This 
remarkable belt, the Milky Way," says Sir John Her- 
schel, " when examined through powerful telescopes, 
is found to consist entirely of stars, scattered by mil- 
lions, like glittering dust, on the black ground of the 
general heavens." The most remote stars in our 
firmament Herschel estimates to be at the distance of 
ten thousand billions of miles. Light, which moves 
with the velocity of two hundred thousand miles in a 
second, would require more than one thousand six 
hundred years to traverse this mighty interval. And 
yet these stars are comparatively our near neighbors ; 
they are, as it were, the dwelling-houses of our own 
village. 



Give Herschel's description of the P4ilky Way. At what distance 
from us are the most remote stars in our firmament ? With what 
rapidity does light move ? How long would it take light to traverse 
this interval ? 



OBSERVATION. 105 



CHAPTER VIII. 



OBSERVATION. 

In the preceding" chapters, the object has been to 
present a simple view of the great facts of Astronomy, 
as they exist absolutely, without regard to the position 
of the eye which observes them, or the state of the mind 
which reasons upon them. The magnitudes, positions 
and movements of the heavenly bodies have been pre- 
sented to view, as they would appear to an observer 
capable of moving, at will, among them, or of taking 
some commanding position, from which he could sur- 
vey the whole in one general view, or examine each 
part in detail, from stations the most advantageous for 
the purpose. 

But all this knowledge, so distinct and simple, when 
thus presented in a general view, has had to be very 
slowly gathered, step by step, by mankind. It has 
required more than two thousand years of time, and a 
vast amount of labor, to attain it. The reason is, that 



What has been the object in the preceding chapters of this work ? 
In what point of view have the magnitudes, positions and motions of 
the heavenly bodies been presented ? How is it said that this know- 
ledge had to be acquired ? How long has it taken to attain it ? 

5* 



106 THE YOUNG ASTRONOMER. 

the motions of the heavenly bodies, though very 
simple in themselves, are often very complicated and 
mysterious in appearance, as they present themselves 
to an observer stationed on the Earth — where, of course, 
all observers have been stationed, who have furnished 
us with any knowledge on this subject. Now it is im- 
portant that the pupil should understand not only the 
results to which the science of Astronomy has at length 
arrived, but also something of the appearances which 
the heavenly bodies exhibit to a spectator on the Earth, 
from which these results have been slowly deduced — 
and something of the nature of the instruments and 
arrangements by which the investigations have been 
made — and also of the practical purposes to which the 
results of Astronomical science are applied. It is, in 
fact, in these points of view that Astronomy will pre- 
sent itself most frequently to our attention, in the course 
of life. For when we look upon the heavens ourselves, 
we see, not the simple movements which exist in real- 
ity, but the complicated and deceptive appearances, 
which bewildered philosophers so long. And in our 
intercourse with others, the aspect in which topics con- 
nected with Astronomy will present themselves in con- 
versation, will almost always relate to these appear- 
ances, to the plans and arrangements of men for ob- 



What has been the cause of this ? How many things are mentioned 
which it is important that the pupil should understand besides the re- 
sults to which the science of Astronomy has arrived ? What is the first ? 
What is the second ? In which of these points of view will a knowledge 
of Astronomy be the most useful ? When we look upon the heavens do 
we perceive the simple movements which the planets are now known 
to make ? What do we perceive ? What relations of Astronomy most 
frequently become topics of conversation in the intercourse of life I 



OBSERVATION. 107 

serving them, and to the practical advantages which 
they derive from the results. 

If we suppose a spectator looking, for the first time, 
into the heavens, in a clear night, and taking a survey 
of the firmament, it is easy to see that his first impres- 
sion would be that he was looking upon a vast concave, 
studded with shining points, of various degrees of bril- 
liancy, placed entirely without order, and all in a state 
of repose. If, after waiting a few hours, the observer 
were to come and view the stars again, he would find 
that he had been mistaken in supposing them to be in 
a state of repose, for it would then be seen that the 
whole canopy had advanced from the east towards the 
west, so as to bring those stars which before were in 
mid-heaven towards the western horizon, while those 
which before were in the east would have risen higher, 
and those which had been near the western horizon 
would have passed below the horizon, out of view. 
Any one can observe these appearances any evening, 
by noticing, at an early hour, the positions of stars 
and groups in various parts of the sky, and then, at a 
later hour, looking again, when he will see that a 
change has taken place in their positions, not in respect 
to each other, but in regard to the horizon and to the 
meridian. 

In order to make such observations as these in an 
intelligent and scientific manner, it is necessary for the 



What would be the appearance presenting itself to the eye of a 
spectator looking for the first time at the heavens ? What change 
would he observe after the lapse of a few hours ? How can these ap- 
pearances be easily observed ? What line is mentioned which it ia 
important that the pupil should distinctly understand ? 



108 THE YOUNG ASTRONOMER. 

pupil to understand practically what the meridian is. 
Let the observer direct the finger to the point exactly 
over his head. This point is called the zenith. It is 
obvious that from this point the finger may be moved 
down to the horizon in any direction, north, south, 
east or west. The distance from the zenith down to the 
horizon, at any point of the compass, is obviously one 
quarter of a circle, or 90 degrees. The distance from 
that point of the horizon, whatever it may be, up to the 
zenith, and thence down to the opposite point of the ho- 
rizon, being half a circle, or 180 degrees. Now if the 
finger be moved in this manner from the zenith down 
to that point of the horizon which is exactly south of the 
observer, it will trace the line of the meridian of that 
observer. All the stars which pass south of the observer 
will cross this meridian at right angles. The Sun 
crosses it every day at noon. It is to be understood 
that the line of the meridian continues through the 
northern part of the firmament in the same manner. 
It passes from the zenith northward through the pole, 
and thence to the point of the horizon which is exactly 
north of the position of the observer ; and all the stars 
which are too far to the northward to pass south of the 
zenith, cross this part of the meridian at every revolu- 
tion. It is, however, that part, of the meridian which 
is south of the observer that is most important, as it is 

What is the zenith ? What is the distance in degrees from the ze- 
nith to the horizon ? How large a part of a circle is it ? In which 
direction must the finger be moved from the zenith to the horizon to 
indicate the meridian ? In what manner do the Sun and stars cross 
the meridian ? Does the meridian extend beyond the zenith towards 
the north ? W hich part of the meridian is most important, that which 
is north or that which is south of the zenith ? 



OBSERVATION. 109 

this part which the Sun, the Moon, the planets, and 
those stars whose motions are most frequent subjects of 
observation, cross in their diurnal revolutions. 

The reason why the meridian comes to be a line of 
so great importance in astronomical observations is 
this, viz., that it is possible to determine the time when 
a heavenly body crosses the meridian far more exactly 
than it can be determined when it passes the horizon, 
whether in rising or setting. This may appear strange, 
since the horizon is a visible reality, while the meri- 
dian is only an imaginary line, with nothing to mark its 
place in the heavens. But the horizon is not exactly 
marked, except at sea ; the outline of the land being al- 
ways more or less irregular. Then the horizon is more 
frequently obscured by mists and vapors, or by a gen- 
eral haziness, which conceals the celestial object from 
view. Then again, in looking at an object near the 
horizon, we look through a great extent of the Earth's 
atmosphere, by means of which a very deceptive re- 
fraction is produced, which does not take place when 
we look directly out of the atmosphere, as we do when 
observing an object in mid-heaven. Astronomers, 
therefore, always consider the revolution of a heavenly 
body as beginning and ending when it crosses the me- 
ridian, and not when it rises or sets. They use, in ob- 
servatories, a telescope adjusted with great care to the 

What is it that makes the meridian so important a line ? Why should 
this appear strange ? How many reasons are given why the horizon 
is a less definite line than the meridian ? What is the first reason ? 
The second reason ? The third reason ? At what point do Astrono- 
mers consider the daily revolution of a heavenly body as commencing 
and ending ? What instrument is used in observatories to determine 
when a heavenly body passes the meridian ? 



110 THE YOUNG ASTRONOMER. 

meridian of the place, with a very fine wire, like a hair, 
passing down across the field of view, as exactly as 
possible in the centre of it, and thus they can mark the 
moment when a star or the edge of the Sun passes this 
hair, far more accurately than they could the time of 
its rising or setting. 

When the person who is making observations upon 
the stars is anywhere upon the equator of the Earth, 
the Sun and stars all appear to rise perpendicularly in 
the east — that is, at right angles to the horizon ; and 
mounting the heavens in direct lines, they cross the 
meridian, and then descend in the west, perpendicu- 
larly, as they rose. In going from the equator towards 
the north pole, it is evident that these circles of motion 
described by the stars will decline more and more 
towards the south. Thus in the latitude of the United 
States the stars which rise exactly in the east will not 
rise perpendicularly and pass over the zenith, but 
will decline towards the south, passing round in an 
oblique circle, more or less oblique according as the 
position of the observer is more or less to the north- 
ward. At the pole of the Earth, the pole of the 
heavens would be exactly over the observer's head, 
and all the heavenly bodies would revolve in circles 
parallel to the horizon. 

It is not possible actually to reach the pole. But 



What is it in this telescope which marks the meridian ? Suppose 
an observer of the stars is upon the Earth's equator, how will they 
appear to rise ? What change takes place in these apparent motions 
as the observer goes towards the north ? What will be the appear- 
ances anywhere in the United States ? What would be the appearance 
at the pole ? Is it possible actually to reach the pole ? 



OBSERVATION. Ill 

navigators have succeeded in forcing their ships through 
the openings in the ice, in the summer months, to 
within a short distance of it ; and there they find that 
the Sun goes round and round the horizon, nearly, 
though not quite, parallel to it. In the summer he is 
above the horizon, and in the winter, when he is far- 
ther to the southward, he is below it. So that for six 
months it is continual day, and for six months con- 
tinual night. Or rather it is continual morning and 
continual evening ; for as in the summer he never 
rises far above the horizon, and in the winter never 
goes far below, but only passes round and round just 
above or just below, the long day has always the ex- 
pression and appearance of morning just after sunrise, 
and the long night that of evening just after sunset. 

An observer in the United States would find the 
Sun, like the stars in the same latitude, always passing 
round from the east to the west in an oblique course 
declining to the south. The path which it describes 
one day is always parallel to that which it describes 
on another, though farther to the north or to the south, 
according to the season of the year. Of course, when 
the Sun is farthest to the north, it rises higher in the 
middle of the day, and passes the meridian at a higher 
altitude, as it is called — that is, at a greater distance 
from the horizon. In the winter, when the Sun is far- 



How have navigators succeeded in getting near to it ? What do 
they find to be the apparent motions of the Sun and stars there ? 
What effect does this have upon the day and night ? What is the 
nature of the motion of the Sun, as seen in the United States ? In 
which season of the year does it pass the meridian at the highest 
point ? 



112 THE YOUNG ASTRONOMER. 

ther to the south, it passes round in a lower circle, but 
in one which is still parallel to the other. It of course 
crosses the meridian at noon at a lower point, and has, 
at that time, a less altitude. 

The term altitude is used to denote the distance of a 
body above the horizon, measured in degrees, and it 
is a term very frequently employed in astronomical 
operations. It is important that the pupil should have 
a clear idea of its meaning. The distance from the 
horizon up to the zenith is a quarter of a circle, or 
ninety degrees ; so that a star precisely in the zenith 
would have an altitude of ninety degrees. A star half 
way between the horizon and the zenith would have 
an altitude of forty-five degrees. One-third of this 
last distance would, of course, be represented by fifteen 
degrees. It would be a very useful exercise for the 
pupil, with these data in mind, to estimate the alti- 
tudes of various stars as seen in the heavens, both w r ith 
a view of fixing permanently in the mind the precise 
import of the term, and of gaining some practical idea 
of the distances which would be thus compared with 
each other. 

It is important not to confound the word altitude 
with latitude. The latter is derived from a Latin word 



At which season has it the least altitude when crossing the meri- 
dian ? What is altitude ? What is the distance in degrees from the 
horizon to the zenith ? What then would be the altitude of a star in 
the zenith ? What would be the altitude of a star half way between 
the zenith and the horizon ? What exercise is recommended as use- 
ful to the pupil in this connexion ? Point to the horizon. Point to 
the zenith. Point to an altitude of about forty-five degrees. Point 
to an altitude of about forty degrees. Of about twenty degrees. 



OBSERVATION. 113 

which means side, and it denotes the distance which a 
place upon the Earth's surface is, upon one side or the 
other of the Earth, reckoning from the equator. The 
other term is derived from a Latin word meaning high, 
and denotes the elevation of an object in degrees, 
measured from the horizon. Thus we say that in high 
latitudes , meaning far to the north, the Sun never 
attains a great altitude, but passes around the horizon 
at a short distance above or below it. 

On observing the heavenly bodies in different lati- 
tudes, we find that they rise, ascend and cross the 
meridian, and then descend and set, in circles more or 
less oblique according to our distance from the equator 
— nearly all of them, however, preserving the same 
relative position. That is, if a group or cluster of stars 
rise together, presenting to the eye a certain configura- 
tion, they pass on together, crossing the meridian and 
descending in the west, preserving all the time the 
same relative position in respect to each other. The 
next evening the same group rises again, presenting 
precisely the same configuration as before, and in the 
same position in respect to surrounding groups. Thus 
the stars have continued their revolutions, without 
changing their places in respect to each other, so far 
as the human eye can perceive, during all the centu- 
ries which have elapsed since they w r ere first observed. 

This fixedness in respect to each other does not, 
however, apply to quite all the stars. As has already 



What is the distinction between the altitude and latitude ? What 
is meant by the stars preserving the same relative position ? What 
appearances does any observed group of stars present on successive 
evenings ? Are all the stars thus fixed in relation to each other ? 



114 THE YOUNG ASTRONOMER. 

been explained, there are a few which wander about 
among the rest. When these wandering stars were 
first observed, their strange and mysterious motions 
were the subject of continual wonder. Sometimes 
they would move backwards and sometimes forwards — 
sometimes fast and sometimes slow. The motions of 
these bodies are however now fully explained by the 
Copernican system ; their wanderings being all ac- 
counted for by the combined effect of their own motion 
and ours, as all revolve around the common centre, 
the Sun. 

To make a map of the stars, and to mark upon it the 
wanderings of a planet, it is only necessary to contrive 
some instrument for measuring their distances from each 
other, and then marking their places upon a sheet of 
paper at these distances. Ferguson, a celebrated Astron- 
omer, when a boy, contrived a very simple instrument 
for this purpose. It consisted simply of a thread with 
a little knot near one end, and a small bead upon it. 
This bead could be slipped along the thread, and 
would remain at any part where it was placed. By 
holding this thread out at arm's length, the apparent 
distance of two stars could be measured, by bringing 
the little knot to correspond with one of the stars and 
then slipping the bead till it corresponded with the 
position of the other. In doing this, the string was to 
be held at arm's length against the sky. When the 



What appearance do the wandering stars present in respect to their 
motions ? Are all these wanderings now explained ? What is neces- 
sary in order to make a map of any particular portion of the heav- 
ens ? What plan did Ferguson adopt when a boy ? How was this 
apparatus used ? How was the string to be held ? 



OBSERVATION. 115 

bead was thus adjusted upon the string so as to corre- 
spond with the distance of some star from another star, 
the string was laid down upon the sheet of paper and 
two dots made upon the paper, corresponding with the 
knot and with the bead. Thus the apparent places 
of the two stars were indicated upon the paper. 

To find and mark the position of a third star, it was 
necessary to measure its distance from both the others, 
in order to determine its position in relation to both. 
This, with a little practice, can be easily done; and 
young Ferguson was accustomed to make very neat 
and pretty maps of the constellations by measuring the 
sidereal distances in this way. The correctness of the 
result, in using such an apparatus as this, will depend 
mainly upon the observer's extending his arms equally 
at each successive measurement, so as to have the 
thread always at the same distance from the eye. For 
when the thread is held near the eye, any given length 
will cover a much larger distance in the sky than 
when it is held out far from it. 

Altitudes, as well as other distances, may be mea- 
sured by such a thread as this. If the observer takes 
the knot between the finger and thumb of the right 
hand, and holds it over his head, and then slips the 
bead down until it is opposite the horizon, keeping 
the arms extended, so as to have the thread as far as 

How were the distances thus ascertained transferred to paper ? 
How many measurements are necessary in order to ascertain the posi- 
tion of a third star, after two have been laid down upon the map ? 
What does the correctness of the result in these measurements mainly 
depend upon ? Why ? Can altitudes as well as other distances be 
measured by this apparatus ? How can the bead be adjusted so as to 
represent a distance of ninety degrees ? 



116 THE YOUNG ASTRONOMER. 

possible from the eye, the length included between 
the knot and the bead will correspond with the dis- 
tance of ninety degrees. If now the thread be doubled 
upon itself, to find the middle of it, and the bead be 
slipped to the middle point thus found, the distance 
then from the bead to the knot will represent forty- 
five degrees; and by this measure the observer can 
easily ascertain what stars are about forty-five degrees 
from the horizon. In the same manner the thread 
might be subdivided farther, and the points marked by 
little colored threads, introduced with a needle, so as to 
make it answer the purpose of measuring approxi- 
mately a great number of altitudes and distances. Of 
course, the results would be very far from being accu- 
rate, as this method of measurement is liable to many 
sources of error. It is sufficiently accurate, however, 
for the purpose here intended, viz. : to give the pupils 
who might use it a correct idea of the nature of the 
quantities thus measured, and to familiarize them with 
the terms used in speaking of them, and also to enable 
them, when in their reading or in conversation they 
hear distances in degrees and minutes mentioned, to 
form some practical conception of the import of such 
expressions. 



How to represent a distance of forty- five degrees ? Can accurate 
measurements be made by this apparatus ? What advantages, then, 
will result from the use of it ? 



INSTRUMENTS AND OBSERVATORIES. 117 



CHAPTER IX. 



INSTRUMENTS AND OBSERVATORIES. 

Such an apparatus as was described in the last 
chapter is of no service for obtaining correct results or 
measurements. It will only answer to aid the pupil 
in forming clear conceptions of the nature of the ope- 
rations and measurements themselves. 

For the practical purposes of Astronomy, it is neces- 
sary that instruments of the greatest exactness and 
nicety of construction should be provided. The place 
in which they are used must also be suitable. The 
instruments must rest upon a solid foundation, where 
they will not be subject to any tremor or jar, and 
must be placed in buildings where they will be 
protected from injury, while yet openings are pro- 
vided which will allow of examining every part of the 
sky. An establishment fitted up thus for astronomical 
observations is called an observatory. Some observa- 
tories are public, being built, furnished and sustained 
at the expense of governments. Some are private, 

What is the only advantage to be derived from such an apparatus 
as was described in the last chapter ? What is said to be essential 
for the practical purposes of Astronomy in respect to instruments ? 
In respect to the place where they are used ? What is such a place 
called ? What two classes of observatories are mentioned ? 



IIS 



THE YOUNG ASTRONOMER. 



being the property of gentlemen interested in Astron- 
omy as a pleasurable pursuit. 

The observatory most known in the English world 
is the Royal Observatory at Greenwich. Green- 
wich is a town a few miles below London, on the 
Thames. The observatory is situated on rising ground, 
back from the river, and is celebrated for the long 
series of exact observations which have been made 
there, and for the eminent Astronomers who have 
been connected with it. There are public observato- 
ries also in many other parts of Europe and in the 
United States, some connected with governments, and 
others with literary institutions. At these observato- 
ries a great variety of instruments are set up, for mak- 
ing the different observations required. 

The telescope is the great instrument of Astronomy, 
and it is constructed on the following principles. 

When we look at an object with the naked eye, it 
is only that small portion of the light coming from it 
which can enter at the pupil, which furnishes us with 
the means of vision. Now, the essential object of 
the telescope is to gather together a larger beam of 
rays, and then, by means of glass lenses, or mirrors, 
bring them into the eye in the proper condition for 
producing distinct vision. There is, therefore, in a 
telescope always one large glass, or large mirror, to 



What is the most celebrated observatory in the English world ? 
How is it situated ? What is said of other observatories ? What is 
the great instrument of Astronomy ? When we look at an object with 
the naked eye, what portion of its light only is available for produc- 
ing vision ? In what manner does the telescope increase this sup- 
ply? 



INSTRUMENTS AND OBSERVATORIES, 119 

collect the rays. There is also, besides this, a series 
of smaller glasses, to change the directions of the rays 
after they are gathered, so as to cause them to enter 
the eye in a proper manner to produce a distinct 
image, or else to vary the nature of the image, accord- 
ing to the wish of the Astronomer. For exam- 
ple, one set of small glasses will make the image 
larger, but more faint ; another will make it smaller, 
and more bright ; — both sets depending entirely for 
what they can do on the quantity of light gathered 
for them by the large lens, or large mirror, which first 
receives the rays. 

Those telescopes which gather light from the object 
to be viewed, by means of a mirror , are called reflect- 
ing telescopes, or reflectors. In the smaller reflecting 
telescopes in use, the mirror for gathering the rays of 
light is from a few inches to a foot in diameter. This 
mirror is commonly called a speculum. The celebrated 
great telescope of Herschel had a speculum four feet 
in diameter. The tube of this telescope was forty feet 
long, and the observer sat in a little gallery attached 
to the upper end of it, and looked down into the tube, 
the great reflector being at the lower end. To support 
so large a tube, and to furnish the means of moving 
it, so as to direct it to any part of the heavens, required 
a very complicated and heavy frame-work, and the 

What other glasses, or mirrors, are required ? What objects do 
these secondary glasses or mirrors accomplish ? What are those 
telescopes called which gather a supply of light by a mirror ? What 
name is given to this mirror ? How large was the speculum in Her- 
schel's large telescope ? How long was the tube ? What was the po- 
sition of the observer in using the instrument ? Where was the spe- 
culum placed ? How was the instrument supported and moved ? 



120 THE YOUNG ASTRONOMER. 

whole was necessarily placed in the open air. It re- 
mained for some years, when at length the frame 
decayed, and it was taken down. 

Since this time the Earl of Rosse, an English noble- 
man, has constructed a reflector much larger than Her- 
schel's. The speculum is six feet in diameter, and 
the tube is fifty -six feet long. It is placed in the open 
air, with high walls on three sides of it, and it is sup- 
ported in its proper position by chains. The cost of 
this instrument has been about fifty thousand dollars. 

From the nature of reflection it is obvious that in all 
telescopes constructed on this principle, the speculum 
must be placed in the end of the instrument farthest 
from the object, and unless there is a second reflector 
the observer must turn his back to the object, and look 
into the telescope from the outer end. Unless the tel- 
escope is very large, a considerable portion of the light 
would be intercepted by this arrangement. In small 
reflectors there is, accordingly, a small mirror placed 
near where the eye of the observer would come, on the 
preceding plan, and the rays are reflected by this mir- 
ror back through a hole, made for the purpose, in the 
centre of the great speculum. A little tube, contain- 
ing the proper eye-glasses, is screwed to this orifice on 
the back side, and the observer then views the object 
directly, as in ordinary glasses for land objects. 



What became of the instrument at last ? How large is the specu- 
lum of Lord Rosse's telescope ? How long is the tube ? How is it 
mounted ? What must always be the position of the speculum in the 
telescope ? Where would the eye of the observer naturally come ? 
By what contrivance is the place for the eye of the observer carried to 
the other end of the instrument ? 



INSTRUMENTS AND OBSERVATORIES. 121 

The great difficulty in the manufacture of reflecting 
telescopes is in making the great speculum. It must 
be of metal, for a glass mirror always gives a double 
image, one reflection taking place from the front sur- 
face, and one from the back. This effect is not very 
striking in a parlor mirror, reflecting only the objects 
in the room, — though any one who examines the 
image of any small bright object in such a glass, will 
perceive that the outlines are double, and a telescope, 
constructed with such a mirror, would give a distinct 
double image of every star which it should be brought 
to bear upon. The speculum must be therefore metal- 
lic, so as to have but one reflecting surface. The com- 
position must be such as to bear a very high polish, 
and yet not be too hard, so as to make the labor of 
grinding and polishing it too excessive. It must also 
be of such a nature as not to tarnish by exposure to 
the atmosphere, nor crack from the effect of changes 
of temperature. The mechanical difficulties of casting 
and managing so large a mass as that of some reflect- 
ors which have been made, are very considerable. 
HerschePs great reflector, four feet in diameter, 
w r eighed about two tons. That of the Rosse telescope 
weighs four tons. To prevent such castings from 
cracking it is necessary to cool them very slowly. 
This process is called annealing. The great mirror of 



What is the great difficulty in the manufacture of reflecting tele- 
scopes ? Why will not glass reflectors answer ? How may the double 
reflection of a glass mirror be made evident ? What effect would a 
glass reflector have upon the appearance of a star ? What are some 
of the properties which the metal used must have ? How heavy was 
HerschePs great reflector ? How heavy is Lord Rosse's ? 
6 



122 THE YOUNG ASTRONOMER, 

• 

the Rosse telescope, as soon as it was cast, and while 
yet red-hot, was rolled, upon a railway prepared for 
the purpose, into a heated oven, where it was left six- 
teen weeks to anneal. 

There is another great objection to the use of a 
reflector to collect the light from an object for tele- 
scopic purposes, and that is that only a part of the 
light so collected is reflected — the remainder being 
dissipated or absorbed at the reflecting surface. For 
this and other reasons, a glass, of the form of those 
used under the name of sun-glasses, provided it be per- 
fect, is better for the purpose of collecting rays of light, 
than a reflector of the same size. Such glasses are 
called lenses. A lens which is thicker in the middle 
than at the edges, so as to have its surfaces convex, 
is called a convex lens. This is the case with the 
glasses of such spectacles as aged persons wear. The 
effect of such a lens is to draw the rays of light toge- 
ther — that is, the rays converge after passing through 
it, and meet in a point called the focus. If the lens is 
thinner in the middle than at the sides, so as to make 
the surfaces concave, it is called a concave lens. This 
is the kind of lens used in the spectacles which near- 
sighted persons wear. The effect of this kind of lens 



How long was Lord Rosse's speculum in cooling ? Why was it ne- 
cessary to cool it so slowly ? What other objection is there to the use 
of a reflecting surface as a means of collecting light ? What other 
means is there of accomplishing the purpose ? What is the name 
given to a lens which is thicker in the middle than at the sides ? What 
is the effect of such a lens upon the rays of light ? What is the point 
called to which such rays converge ? What is the name of a lens 
thinner in the middle than at the edges ? What is its effect upon the 
rays of light ? 



INSTRUMENTS AND OBSERVATORIES. 123 

is to disperse or scatter the rays which pass through it. 
The different effects produced by these different kinds 
of lenses may be made manifest by holding two pairs 
of spectacles, one of each kind, to the sun, and receiv- 
ing the rays, after they pass through the glasses, upon 
a sheet of paper, as a screen. By holding the paper, 
at first, very near the glass, and then gradually with- 
drawing it, the different effects of the two glasses will 
be very apparent, the bright spot upon the paper 
expanding, in the one case, as the rays scatter — and 
gradually contracting, in the other, until the rays meet 
in the focus. To make the experiment quite satisfac- 
tory, a sheet of paper with a hole in it as large as the 
glass, should be placed outside the glass, in each case, 
so as to prevent any rays falling upon the screen ex- 
cept such as come through the glass. The change thus 
produced in the direction of rays by passing through a 
lens, is called refraction. 

The principal lens used in telescopes is a convex lens, 
and is placed, not like the reflector at the inner end of 
the instrument, but at the outer end, so that the object 
is seen through it. Telescopes constructed in this way, 
with a great lens instead of a great reflector, are called 
refracting telescopes, or refractors, — as the others are 
called reflecting telescopes or reflectors. The large 
lens employed to collect the rays of light, in a refract- 
ing telescope, is called the object-glass, as it is placed 
at that end of the telescope which is towards the 



How may these opposite effects be made evident ? What is this 
changing of the direction of the rays of light in passing through a lens 
called ? What name is given to a telescope constructed on this prin- 
ciple ? What is the great lens in a refracting telescope called ? 



124 THE YOUNG ASTRONOMER. 

object. The glass nearest the other end of the instru- 
ment, being the one which comes next the eye, is 
called the eye-glass. 

The great work in the manufacture of a refracting 
telescope, is to form this object-glass ; it being found 
extremely difficult to procure glass of a perfectly uni- 
form texture and of sufficient size, and then to grind 
it to its true form ; for any inequality, either in the 
nature of the glass itself or in its form, will prevent 
the rays converging with that regularity essential to 
the forming of a distinct and well-defined image. 

In former times there was a great difficulty in con- 
structing large refracting telescopes, from the circum- 
stance that the images produced by light coming 
through such lenses as have been described, are always 
surrounded with a little colored fring'e, which fringe be- 
came very conspicuous when the instrument was large. 
A remedy for this was at length discovered. It con- 
sisted in having the lens made of two pieces of glass, 
of different kinds, instead of one. These pieces were 
nicely fitted together, the joining surface of one being 
concave, and that of the other convex. The effect of 
the different kinds of glass was such, that the coloring 
influence of one was neutralized by the other, and a 
colorless image was formed. Such lenses are called 
achromatic j which signifies without color. Since this 
discovery, it has been found better to make most tele- 

What is the glass next the eye called ? What is it that requires the 
most delicate work in the manufacture of a refractor ? What are the 
two sources of difficulty ? What objection formerly existed to the 
use of such instruments ? How has this evil been obviated? What 
name is given to those instruments which are constructed in this way ? 
On what account is a lens preferable to a mirror ? 



INSTRUMENTS AND OBSERVATORIES. 125 

scopes in this way, as a much larger portion of the light 
is lost when it is reflected from a mirror than when it 
is refracted by a lens. On this acount it is not neces- 
sary to make lenses used as object-glasses nearly as 
large as the reflectors used in the reflecting telescopes. 
Very few reflectors have ever been made with a lens 
more than ten or fifteen inches in diameter. 

It requires some experience and skill to use a tele- 
scope as w^ell as make one, as there are many difficul- 
ties to be guarded against or surmounted. In the first 
place, the telescope must have a very firm and stable 
footing, for it magnifies its own tremors as well as the 
objects which it aids us to view. Tremors which are 
entirely insensible to our unassisted observation, be- 
come very great in their influence upon such an instru- 
ment. The vibrations produced by the wind upon the 
walls of an ordinary building, and the jars occasioned 
by the passing of carriages in a street, will be sufficient 
to make the stars dance in the field of view of a tele- 
scope so as to make it impossible to get any distinct view 
of them. For this reason, a high position is not favor- 
able for astronomical observations, excepting for such 
observations as are made with the naked eye, an in- 
strument requiring a more solid support than can gen- 
erally be obtained upon a roof or a cupola. In most 
observatories, in fact, there is a solid mass of masonry 
built from the ground, upon which, as a foundation, 



What is the size of the largest lenses which have been constructed ? 
In using a telescope, what is necessary in regard to its position ? Why 
is it necessary to give such an instrument a very stable position ? 
What kinds of jars and tremors are ordinary buildings subject to, 
which would interfere with telescopic observations ? 



126 THE YOUNG ASTRONOMER. 

the instruments rest. The floor upon which the ob- 
server and his attendants walk, is made independent 
of this, so that the tremors occasioned by their move- 
ments may not be communicated to the instruments. 

A second difficulty which an inexperienced observer 
finds in his way, in first using- a telescope, is in 
adjusting it to his eye. The tube which contains 
the small glasses next the eye, has to be drawn 
out a little, sometimes more and sometimes less, 
according to the distance of the object which is 
to be observed, and also according to the condition 
and structure of the observer's eye. This last is 
the most difficult ; for if the instrument had only to 
be adjusted to the object, one person who was more 
skillful and experienced, could make the adjustment 
for another who was less so. But when it is properly 
adjusted to the object to be viewed, so that one indi- 
vidual can see it distinctly, if another, whose eye is a 
little different, attempts the observation, the image 
will be indistinct, and he will have to move the tube 
in or out a little, by means of a screw, before he can 
see plainly. This requires a care and a precision which 
many persons fail to exercise at their first attempts to 
use such an instrument ; and after looking through it 
for a time they either perceive that they do not get a 
distinct view, and after repeated efforts get discouraged 
and abandon the attempt, or else, after gazing a mo- 
ment at the dim or confused images which they per- 

What difficulty is there in the adjustment of the instrument ? Can 
one person adjust it for another ? Why not ? Are persons always 
successful when they first attempt to look through a telescope ? In 
what two ways does the experiment sometimes result ? 



INSTRUMENTS AND OBSERVATORIES. 127 

ceive, go away, imagining that that is all that is to be 
seen. 

The state of the atmosphere is also of great im- 
portance to be attended to in astronomical observation. 
Often, when the weather is not cloudy, there is a dim- 
ness in the air, and oftener still a waving motion of 
currents which disturbs the vision. Herschel thought 
that there were not more than one hundred hours in a 
year in England really favorable for the observation 
of celestial phenomena by telescopic instruments. 

There is another difficulty which often surprises 
those who, for the first time, attempt observations with 
the telescope, and that is the difficulty of finding the 
object, or rather of bringing it into the field of view 
of the telescope : for, it must be observed that the in- 
strument magnifies spaces as well as objects of vision, 
and the region of the heavens brought into view by 
it, in any one position, is only a very small space, 
greatly expanded by the power of the instrument. If 
the observer wishes to look at a particular star, and 
points the instrument towards it, judging of its direc- 
tion only by the eye, the probability is that it will de- 
viate far enough to one side or the other, to throw the 
star out of the field of view. There is a very simple 
contrivance which obviates this difficulty. It consists 
in attaching a small telescope to the side of the larger 

What is said of the state of the atmosphere in such observations ? 
Is it sufficient that it be not cloudy ? What are the other causes of 
obscuration ? How much time did Herschel think could be calcu- 
lated upon, on the average, in England, as really favorable to such 
observations, in a year ? What is the difficulty in respect to finding 
the object ? What is the cause of this difficulty ? In what way is it 
remedied ? 



128 THE YOUNG ASTRONOMER. 

one. This small telescope is called a finder, and as it 
magnifies but little, a star or other object is easily found 
in it. Across the field of view of this small telescope 
are two cross hairs, and when the whole instrument is 
adjusted to such a position as to bring the star at the 
intersection of these cross hairs, in the small telescope, 
it will be sure to come somewhere within the field of 
view of the larger one. 

It follows, also, from the nature of the magnifying 
powers of a telescope, that it must magnify motion, as 
well as magnitudes and space, and accordingly the 
apparent motion of a star is much greater across the 
field of view of a telescope, than when seen by the 
naked eye. This requires a very frequent movement 
of the instrument to follow it and keep it in view. 

The most striking and interesting objects to be viewed 
by means of large telescopes, are the planet Venus, 
which appears like the moon in some of its phases ; 
Mars ; Jupiter, with his belts and his moons ; the rings 
and the moons of Saturn ; the Earth's moon, espe- 
cially when the Sun shines upon its surface in such a 
manner as to cause its elevations and depressions to 
cast strong shadows ; the spots on the Sun ; comets ; 
and lastly, some nebulae and clusters of distant stars. 

Besides these large telescopes, intended mainly to 
view objects in the heavens, there are others employed 
by astronomers, which are mounted in various ways, 
with, arcs very precisely divided into degrees, minutes 



What is said in regard to the motion of a star across the field of 
view of a telescope ? What are some of the most interesting objects 
to be viewed by a telescope ? What is a transit instrument ? How 
is it mounted : 



INSTRUMENTS AND OBSERVATORIES* 129 

and seconds, for measuring accurately various celestial 
magnitudes and distances. Sometimes such a tele- 
scope is mounted in such a way as to point always to 
the meridian, but poised in such a manner that it may 
be elevated or depressed to any degree of altitude. 
This is called a transit instrument. Of course the 
mounting of a transit instrument does not allow of its 
being directed to the eastern or western region of the 
sky. It is confined to the meridian, and it has a hair 
passing down across the field of view which marks 
the precise meridian of the place ; and thus the mo- 
ment when a star crosses this hair will be the precise 
moment of its crossing the meridian. Observations 
of the time when bodies thus pass the meridian are 
among the most important of all astronomical observa- 
tions. A great many problems, measurements and 
investigations depend upon them. The transit instru- 
ments, therefore, in all observatories, are adjusted with 
great care. In the great observatory at Greenwich 
there is a particular room called the transit room, 
where there is a large telescope placed firmly upon a 
stone foundation, and adjusted with great precision, so 
as to move only in the meridian. The object-end may 
be raised or depressed to any angle, but it cannot 
move to the right or left ; so that whatever its position 
may be, the cross hair passing down through the centre 
of its field of view, marks the meridian in that part of 
the heavens. Behind the instrument is a chair for the 
observer, with a back which may be inclined at any 



How is the precise place of the meridian marked in the field of 
view ? What kind of motion does its mounting allow of ? How is 
the transit instrument arranged at Greenwich ? 

6* 



130 THE YOUNG ASTRONOMER. 

angle, to give him a good position for looking through 
the telescope, at any point of elevation. 

It is obvious that a transit instrument can only mark 
time. It cannot measure distances directly, nor examine 
appearances or phenomena to advantage. For it cannot 
move from one part of the heavens to another, except 
simply up and down in the meridian ; so that it cannot 
directly compare the position of one star with another, 
nor follow a planet or a nebula, so as to keep it in the 
field of view, and examine its appearance at leisure. 
It is only employed to mark the precise time when the 
heavenly bodies, one after another, pass the meridian 
of the place where the observation is made. Certain 
distances can be deduced from the result of transit ob- 
servations, it is true ; for by comparing the time which 
intervenes between the transit of one body and another, 
certain relations of their distance from each other can 
be ascertained. The result always is, however, in the 
first instance, the marking of time ; and for this pur- 
pose, a clock of the most perfect construction possible 
must accompany a transit instrument. It requires two 
observers to make the observations — one to look 
through the telescope at the star, and to give a signal 
at the precise instant when it disappears behind the 
cross hair, and the other to note the time by the clock. 
The necessity for great accuracy in these results arises 
partly from the fact, that the tables by means of which 



Is a transit telescope fitted to measure distances directly, or to sur- 
vey appearances in the heavens ? Why not ? What is the sole and 
simple object which it aims at ? How many observers are necessary ? 
What other instrument is required ? Why is it necessary that the 
observations should be made with so much accuracy ? 



INSTRUMENTS AND OBSERVATORIES. 131 

the place of a ship at sea is determined are all con- 
structed by means of these and similar observations; and 
an error of a part of a second, in the time of a transit, 
might cause an error of many miles in the calculations 
of all ship masters who should depend upon the tables 
affected by such an error. 

Besides telescopes mounted as transit instruments, 
there are others so mounted as to allow of free motion 
in any direction, with various arcs very nicely grad- 
uated, by which the exact extent of every motion 
given them may be ascertained. Some of these have 
clock-work attached to them, which causes them to 
move in such a manner as to keep pace exactly with 
a star or other heavenly body brought into view. In 
this case the observer may sit quietly for hours, if he 
choose, and survey any appearance which attracts his 
attention ; the machinery keeping the object of his 
observation always before him. The motion of such 
a telescope must of course be always parallel to the 
equator, as the heavenly bodies generally move in cir- 
cles of that description. Such an instrument is called 
an equatorial instrument, or simply an equatorial. 



Suppose it is required to mount a telescope so as to follow a star 
and keep it for some time in view, what motion must it have ? What 
is a telescope so mounted called ? What machinery is sometimes 
attached to it ? 



132 THE YOUNG ASTRONOMER, 



CHAPTER X. 



PRACTICAL RESULTS. 

Perhaps the greatest practical benefit which man- 
kind derive from the science of Astronomy, is the aid 
which it renders them in conducting* ships over the 
ocean. A ship, once beyond sight of land, has to rely 
almost entirely upon the heavenly bodies for its guid- 
ance. Of course it becomes necessary that the motions 
and positions of these bodies should be known with 
great accuracy. These motions and positions are as- 
certained, in the first instance, by such observations 
on land as were described in the last chapter. The 
results are recorded in tables, which navigators take 
with them to sea ; and then they ascertain their posi- 
tion by comparing the results of their observations, as 
made from the decks of their ships, with the records 
made in the books of the results of the Astronomers' 
observations on the land. 



What is the greatest practical benefit which mankind derive from 
the science of Astronomy ? Upon what is a ship at sea obliged to rely 
as a means of knowing her position ? What then becomes necessary 
in respect to the motions and positions of the heavenly bodies ? How 
is this effected ? 



PRACTICAL RESULTS. 133 

The instruments on which ship-masters mainly rely 
at sea are two : first, an instrument to measure the 
distance of a heavenly body from the horizon, or of 
one heavenly body from another ; and secondly, an 
instrument to keep the time of London, or of some 
other known place, wherever they go. The most 
common instrument for the former purpose is one 
called a quadrant. It is so called on account of its 
measuring a distance of ninety degrees, which is the 
quarter of a circle. The instrument is small, being 
about a foot in length. It has to be held in the hands 
while making the observation ; for, on account of the 
motion of the ship, no instrument resting upon the 
deck could possibly be used. The quadrant is verj 
complicated in its construction, and requires much 
skill and practice to use it to advantage. The prin- 
ciple, however, on which it is constructed, is sim- 
ple. It is designed to measure the distance between 
twp objects, as, for example, between the Sun and the 
horizon ; and it is so contrived that one of the objects 
is seen directly, through a plain glass, and the other 
reflected through a small mirror. The mirror is mov- 
able, and may be turned until the object seen directly, 
and the one seen in reflection, shall come precisely 
together at the junction between the silvered part and 



How many are the instruments principally required by ship-masters ? 
What are the objects of these two species of instruments ? What is 
the name of the instrument most commonly used for measuring dis- 
tances ? W^hy is it called a quadrant ? How large is such a quadrant ? 
Why could not a stationary quadrant be used at sea ? Is it easy to 
understand and use the quadrant ? Describe the principle on which 
it is constructed. 



134 THE YOUNG ASTRONOMER. 

the transparent part of a small plate of glass, where 
both can be seen. Now the degree to which the little 
mirror has to be turned to effect this junction, shows 
how far distant the two objects are from one another. 
The mirror is attached to an index which moves upon 
a brass or silver arc, on which the degrees and minutes 
are accurately marked, and thus the result of the mea- 
surement is ascertained. 

The sextant is an instrument similar in principle to 
the quadrant; but it measures a greater distance, is 
usually made with greater care, and is more expensive. 
It is used for the larger ships and the more distant 
voyages. 

Every day, when it begins to draw near to twelve 
o'clock, the officers of every ship at sea come upon 
deck, with their quadrants or sextants in their hands, 
to take the Sun's altitude at noon, for the purpose of 
ascertaining the ship's latitude. The latitude of a 
place is its distance from the equator, to the north or to 
the south. Now it is very obvious that in this hemi- 
sphere the farther south the observer is, the higher the 
Sun will rise at noon, when he passes the meridian. 
It is true that the Sun changes his position every day, 
so as to pass the meridian at a different altitude, as 
seen from the same place; but then these changes 
have all been calculated beforehand, by Astronomers, 
upon the land, and tables have been constructed show- 



What is a sextant, and how does it differ from a quadrant ? At what 
time of the day do the officers come on deck to take their observation ? 
What measurement is it that they wish to take ? What effect does 
the position of the observer on the Earth, in respect to latitude, have 
in respect to the altitude of the Sun at noon ? 



PRACTICAL RESULTS. 135 

ing how far the Sun moves to the north or south of 
the equator for every day, hour, minute and second 
of the year ; so that the navigator has the means of 
knowing, from his books, at what altitude the Sun 
ought to cross the meridian for every mile of latitude 
on the Earth's surface, from the equator to the pole, 
and for every day in the year. He has, therefore, on 
any given day, only to ascertain, with his quadrant, 
at what elevation the Sun does pass the meridian where 
his ship is, in order to find from his books how far 
north of the equator the ship must be. 

When it is cloudy this observation cannot be made ; 
and sometimes several days elapse, during which the 
mariner cannot u get an observation," as it is called. 
At such a time, the only means of knowing his posi- 
tion from day to day is by a reckoning of the distance 
and direction of the sailing, since the time when the 
last observation was made. 

But when the altitude of the Sun at noon can be 
obtained, it furnishes a very ready mode of obtaining 
the ship's place in respect to latitude ; and so exact 
are the quadrants in their graduations, and so accu- 
rate are the tables of the Sun's position, contained in 
the books of navigation, that the place of a ship, in 
respect to its distance north or south of the equator, 
can be ascertained with great accuracy — often within 
a mile. 

The place of a ship in longitude is far more difficult 

How does the navigator find the latitude of the place from know- 
ing the Sun's altitude at noon ? What is done when the sky is 
cloudy ? With what degree of accuracy can the ship's place be found 
in latitude when a good observation is obtained ? Is it equally easy 
to find a ship's place in longitude ? 



136 THE YOUNG ASTRONOMER. 

to be determined from observations of the heavenly- 
bodies, though the principle on which it is obtained is 
equally easy to be understood. It is simply to com- 
pare the time of day at the place of observation with 
the time of day at London, at the same instant. This 
is on the principle that the difference in the longitude 
of any two places always corresponds exactly with the 
difference in the time. The reason of this is, that as 
the Earth revolves on its axis by a perfectly equable 
motion, it brings the successive portions of its surface 
to the Sun at periods exactly proportioned to their dis- 
tance from each other in longitude. Of course, the 
difference in time in which two places come to the 
Sun is always a measure of their difference of longi- 
tude. 

This may be made very evident by considering a 
particular example. The Fejee Islands, in the Pacific 
Ocean, are just about half round the world, measur- 
ing from London. Of course, when it is noon at Lon- 
don it is midnight at the Fejee Islands. Now, sup- 
pose a person at these islands, not knowing in what 
part of the world he was, could in some way learn at 
midnight there, that it was, at that time, exactly noon 
at London ; he could easily infer that he must be pre- 
cisely on the opposite side of the Earth. In other 
words, by knowing that there was twelve hours' differ- 
ence in the time when the Sun would be on the meri- 

What is the principle on which the distance between two places, 
in longitude, is found ? Why is it that the difference in time of any 
two places always corresponds to the difference in longitude ? What 
islands are mentioned which are half way round the world from Lon- 
don ? This being the position of those islands, what time will it be 
there when it is noon at London ? 



PRACTICAL RESULTS. 137 

dian of the two places, he would be sure that there 
was 180 degrees of difference in their longitudes. 

In the same manner, if an observer at Calcutta 
were to learn, at noon there, that it was at that instant 
only six o'clock in the morning at London, which 
would be very nearly the fact, he would perceive that 
the distance of the two places in longitude was such 
that it would require six hours for the Sun to pass, in 
his apparent motion, from the meridian of Calcutta to 
that of London. Now, as it requires twenty-four 
hours for a complete revolution of the Sun, six hours 
would represent quarter of a revolution, and conse- 
quently Calcutta must be 90 degrees east of London. 
Since six hours correspond with a distance of 90 de- 
grees, two hours would represent 30 degrees, and one 
hour 15 degrees. Hence, difference of time may be 
always converted into difference of longitude, at the 
rate of one hour to 15 degrees. 

Of course it becomes necessary, in order to ascertain 
how far a place is, in longitude, from London, to know 
the precise time at the place in question, and also the 
time at London at the same instant. The time at the 
ship is easily obtained every day, by observation of the 
Sun. The London time is carried all over the world, 
by means of very exact time-keepers, called chronome- 
ters^ which are set in London, or at some other port, and 

Suppose it were to be ascertained, at noon, in Calcutta, that it was, 
at that moment, six o'clock at London, what might be inferred as to 
the distance of the two places in longitude ? How many degrees of 
longitude are measured by one hour of time ? What is it consequently 
necessary to know, at any place, besides the time at that place, in 
order to know its distance, in longitude, from London ? How is the 
London time known at sea ? 



138 THE YOUNU ASTRONOMER. 

not altered during the voyage. The observatory at 
Greenwich is on a hill back from the Thames, a little 
below the city, at a place where it can be seen from 
many ships in the river ; and in order that all the 
chronometers may take the precise time, before the 
commencement of the voyage, a signal is given from 
the observatory to mark the moment when it is twelve 
o'clock precisely, each day. This signal consists of a 
black ball upon a pole, which rises from the top of 
one of the buildings. The pole passes through the 
ball, and is so contrived that the ball can slide up and 
down the pole for a few feet. The ball rests usually 
at the lower end of the portion of the pole over which 
it slides, where, however, it is plainly visible. Five 
minutes before twelve it slowly rises half way up. 
This is to call the attention of all the ship-masters who 
wish to take the time. At a few seconds before twelve 
it rises the rest of the way, and at twelve precisely it 
falls back to its original position. The chronometers 
thus set, the navigators can carry the London time 
with them wherever they go ; and by comparing it 
with the time of the place they happen to be in, every 
day, at noon, they can always ascertain their longi- 
tude. If their time is before the London time, they 
know they have gone eastward. If it is one hour ear- 
lier, they must have gone fifteen degrees to the east- 
ward. If their time is two hours later than the Lon- 



Describe the arrangement by which the true time is given to the 
ships in the port of London. Suppose the time at the ship is be- 
fore the London time, is the ship to the eastward or westward of 
London ? Suppose a ship finds her time to be two hours later than 
London time, which way and how far is she from London in 
longitude ? 



PRACTICAL RESULTS. 139 

don time, they must have gone thirty degrees to the 
westward, and the same principle applies in all other 
cases. 

The chronometers carried to sea are made with the 
utmost care, as the safety of the ship often depends 
upon their accuracy. They are in the form of large 
watches, and they are set in a box, in which they are 
poised upon two pair of pivots, at right angles to each 
other, so as to allow of easy motion in every direction, 
that they may accommodate themselves to the rocking 
of the ship. They are so exact that they sometimes 
vary from their rate but very few seconds in going the 
longest voyages, and visiting every quarter of the 
globe. 

There are other modes by which the navigator may 
obtain the London time at sea, besides taking it along 
w T ith him in his ship by means of a chronometer. 
The principle on which these other methods are founded 
is this : every change which takes place in the situa- 
tion of the heavenly bodies is known beforehand by 
Astronomers, having been carefully calculated from 
the known laws of the celestial motions. Now, in 
respect to all such changes as can be observed by ship- 
masters at sea, the times when they will occur, as seen 
at London, are accurately noted in tables which the 
navigator takes with him ; and by observing those 
changes at sea, he can learn from his tables what time 
it is at London when they occur. 



How are the chronometers which are used at sea made and 
mounted ? Are there any other modes by which the London time 
can be obtained at sea, besides by means of a chronometer ? Describe 
the method. 



140 THE YOUNG ASTRONOMER. 

The phenomena most in use for this purpose, are 
those connected with the motions of the Sun and Moon. 
The Moon's apparent motion is slower than that of the 
Sun, so that she rises about an hour later each day 
than the day before. When she rises very nearly at 
the same time with the Sun, she cannot be seen ; but 
after a few days, she gets to such a distance that both 
are visible, each in its own quarter of the heavens, as 
long as both remain above the horizon. Now, on ac- 
count of the difference in the rate of motion of these 
two bodies, the distance between them is enlarging or 
diminishing all the time, and the difference is percep- 
tible, by means of good instruments, for every second. 
Of course the navigator can get the exact distance be- 
tween the Sun and Moon at any given moment. Say 
when it is ten o'clock in the morning by his time, he 
then looks into his books to find at what time, at London, 
the Moon was to have been at precisely that distance 
from the Sun; and if he finds that it was at eleven 
o'clock, he infers that he must be fifteen degrees to 
the westward of London. This measuring the dis- 
tance from the Moon to the Sun is called a lunar ob- 
servation. 

There are other celestial phenomena which are 
made use of for this purpose, besides the distance of 
the Sun and Moon ; but the principle is the same in 
all cases. 

The relation between longitude and time, by which 
a difference in the one is always attended by a differ- 

What observation is made for this purpose ? What is this ob- 
servation called? What peculiar phenomenon, in respect to the 
length of the day at sea, results from this relation between longitude 
and time ? 



PRACTICAL RESULTS. 141 

ence in the other, gives rise to a peculiar phenomenon 
in respect to the length of the day at sea, which is 
very familiar to all navigators, but is sometimes diffi- 
cult to be understood by those who are accustomed 
to a fixed residence on land. The phenomenon is, 
that the length of the day — that is, the time from 
one noon to another — is quite different in different 
circumstances. The day at sea is sometimes con- 
siderably less than twenty-four hours long, and 
sometimes considerably more. This depends on the 
circumstances of the motion of the ship. If she is 
going to the eastward, the day is shortened ; if she is 
going to the westward, it is lengthened. The man- 
ner in which this effect takes place may be thus ex- 
plained : 

Suppose a ship to be becalmed at sea, and to be, 
consequently, at rest. It is obvious that it will be 
just twenty-four hours from the time that the Sun 
leaves her meridian, until the time that he returns to 
it again ; in other words, that the length of the day 
on board that ship will be just twenty-four hours. 
But now, if we suppose that the ship, instead of re- 
maining at rest, were driven five degrees to the east- 
ward by a gale of wind, she would have gone so far 
on the way to meet the Sun in his rising the next day. 
It is plain that, by this change of five degrees in her 
place, the Sun has five degrees less than his whole 



Is the day at sea always twenty-four hours in length ? How does 
it vary from this standard ? On what does the variation depend ? 
Suppose a ship remains stationary in a calm, what will be the length 
of her day ? Suppose she moves five degrees to the eastward, will 
she lengthen or shorten her day ? 



142 THE YOUNG ASTRONOMER. 

circuit to perform before he comes to her meridian on 
the second day. Now, as fifteen degrees correspond 
to one hour, five degrees will correspond to one-third 
of that time, or twenty minutes. So that the day, in 
this case, will be twenty minutes shorter than twenty- 
four hours. In other words, it will really be twelve 
o'clock when, by all the watches on board which 
were set right the day before, it is only twenty minutes 
of twelve. 

In the same manner, suppose the ship to go five de- 
grees to the westward, between one noon and ano- 
ther — say between Monday and Tuesday noon. In 
this case, the Sun will have more than a whole revo- 
lution to make, before he can bring to the ship her 
second noon. He will have first to complete one revo- 
lution, which will bring him over the place where the 
ship was on Monday noon. But she will be no longer 
there. She will have moved five degrees farther to 
the west. Of course, the Sun will have this five de- 
grees to traverse before he can again come into the 
meridian of the ship. This will take twenty minutes, 
and this will make the day twenty-four hours and 
twenty minutes long ; so that it will not be really 
twelve o'clock until it is twenty minutes past twelve by 
all the watches on board. 

It follows from this, that the days of all ships sail- 
ing eastward are a little less than twenty-four hours 
long, and those of ships sailing westward are a little 

How much will she shorten it ? Suppose the ship to be going 
westward, will she lengthen or shorten her day ? How will this 
take place ? How much will she shorten it by going five degrees ? 
Are the days of ships going eastward lengthened or shortened ? How 
is it in going to the westward ? 



PRACTICAL RESULTS. 143 

more. The officers, therefore, of a ship going east- 
ward must be on deck by half-past eleven every day, 
with their quadrants, so as to be sure to get the alti- 
tude of the Sun when on the meridian; while those 
who are going westward may wait until their watches 
indicate twelve. 

Astronomy thus contributes very largely to the com- 
fort and happiness of mankind, by guiding the ships 
in which the products of different climes are trans- 
ported to and fro over a boundless waste of waters, 
which, without her aid, would be almost utterly im- 
passable. The accuracy of the tables which she has 
constructed is the result of long series of observations 
and of calculations, involving an amount of labor of 
which the mass of mankind have little conception. 
If these tables and the other records of the celestial 
motions were to be destroyed, it would require many 
years of time, and an enormous expenditure of scien- 
tific labor and research, to open safe ways again over 
the waters of the ocean. 

The study of Astronomy has not only proved of 
vast practical utility to mankind at large, but it exerts 
a very ennobling intellectual influence upon the indi- 
vidual mind which pursues it. It carries the thought? 
away from the objects immediately around us, and 
from the events of the passing hour, to the contempla- 
tion of the immense distances and magnitudes of the 



What is said of the general benefits which mankind have derived 
from Astronomy ? What beneficial effects does the study of Astron- 
omy produce upon the mind ? 



144 THE YOUNG ASTRONOMER. 

heavens, and of the vast periods whose progress and 
duration she records. At the same time, while it 
is thus her peculiar province to deal with all that is 
magnificent and sublime, she trains the minds of her 
votaries to a precision and accuracy, both of thought 
and observation, which no other branch of human 
philosophy pretends to attain. Thus, she connects all 
that is sublime in extent and grandeur with all that 
is beautiful in mathematical exactness and precision. 
She has doubled the comforts of man, by guiding 
his commerce ; she has taught him mathematics, 
and led him to the perfection of his nicest arts ; she 
has awakened in his soul the sublimest thoughts and 
the loftiest aspirations ; she has inspired his poetry 
and kindled his devotion;— so that perhaps the most 
powerful of all the natural influences which have 
operated to elevate and ennoble the human species is 
that which has descended from the stars. 



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